Chapter One

The first thing that Vicki saw when she walked into the TARDIS's control room was Steven Taylor's hand hovering over the central, mushroom-shaped console.

"Don't touch those controls!" she snapped, her voice echoing around the room.

Steven's shoulders hunched defensively, and he glanced towards her. Gradually the echoes of her voice faded away, leaving only the deep hum that meant the TARDIS was still in flight.

"Why not?" he asked truculently, brows heavy, jaw thrust forward. "I'm a qualified space pilot, aren't I? These switches and levers may look complicated, but I'm sure I can figure them out. And the Doctor's been gone for hours. He may never come back. We need to be able to fly this thing." His fingers closed around a large red switch on one facet of the control console. His fingers caressed it hesitantly. It was obvious to Vicki that he hadn't got a clue what he was doing, but didn't want to admit it. "This thing must make us materialize," he added. "Once we've landed, we can take a look around, find out where we are." He sounded as if he was trying to convince himself as much as her.

"I think that's the door control," she said quietly.

He hesitated, his indecisive frown quickly replaced by one of exasperation. "Look, if you've got any better ideas, let me know: Otherwise, trust me for once."

"Why can't we just wait?" she said, already knowing the answer. Because Steven was incapable of waiting for anything, that was why. Because he'd spent so long impotently pacing around his prison cell on Mechanus before the Doctor had rescued him that his patience had been used up. Not that he would ever admit it, of course. Not even to himself. It was odd, Vicki thought as she gazed at Steven's older yet somehow more innocent face, that her time spent stranded had been perhaps the most idyllic of her life. She'd only had Bennett and Sandy the Sand Monster for company on Dido, but she'd been content. Now, although she was learning so much by travelling with the Doctor, that contentment had been lost. Every moment of her life, every person that she met, demanded something of her.

"We can't just wait," Steven explained, breaking her chain of introspection, "because the Doctor might be in trouble. The way he just... just vanished, right in front of us..." He hesitated, and rubbed a hand across his face. He was tired. Tired and scared, Vicki realized. He'd been alone for so long that he found the prospect of taking responsibility terrifying. 'It was like the Doc had been kidnapped.'

"But we haven't explored the TARDIS completely yet," she said, trying to inject a note of calmness into her voice. Getting angry with Steven didn't work - he just grew more stubborn and defensive. "The Doctor could still be here."

"Where?" Steven challenged, hand still on the switch. The door control switch, Vicki reminded herself. She didn't know what would happen if he pulled it while the TARDIS was in flight, but she suspected the results wouldn't be pleasant. "We've checked the bedrooms, the food machine alcove, the lounge -"

"What about the locked doors?" she interrupted. "The Doctor won't tell us what's behind them. There might be more rooms, rooms that the Doctor didn't want us to see."

Steven slammed his fist against the console. "Look, we have to do something! And I still think that if we can just materialize somewhere, we can find a trail, or a clue,"

"And what are you young people doing to my TARDIS?" a peremptory voice demanded from the other side of the console. Steven and Vicki whirled around and gaped at the blurred, fractured bubble of darkness that had appeared - apparently inside the wall - and at the elderly figure within it. "Doctor!" they cried together.

He appeared to be sitting in a triangular framework, and he was frowning at them. Standing, not without some effort, he walked forward. Behind him, both the frame and the dark bubble were pulled apart into a coruscating web of lines which retreated into the far distance until they were lost from sight, leaving only the solid walls of the TARDIS behind the old man's figure.

"Doctor, we were -" Vicki began.

"Where have you been?" Steven demanded.

The Doctor fixed the space pilot with an imperious gaze. "Never mind where I've been," he snapped, "you were about to meddle with the ship's controls, weren't you?"

"No!" Steven protested. "I... I was just trying to -"

"Steven was trying to help," Vicki said calmingly. "You vanished without telling us where you were going. We were worried about you: we thought... Oh, I don't know what we thought. What happened?"

The Doctor's stern expression softened, as she had known it would. The one thing he couldn't resist was wide-eyed concern. "My dear child," he said, "of course you were worried, and I have no right to scold you, hmm? If you must know, I've been... " He frowned. "Well, that's most extraordinary. I can't remember where I've been. The memory has gone. All I can remember is a dandy and a clown. A dandy and a clown." Ignoring the puzzled looks that Vicki and Steven exchanged, he raised a hand to caress his lapel, and appeared surprised to find that he was holding a small white envelope. "Hmm. Perhaps this will tell us something."

As Vicki and Steven watched, he opened the envelope and took out a slip of cardboard. He peered at it for a few moments, then took his pince-nez out of his waistcoat pocket and slipped them on. "Most extraordinary," he repeated, and proffered the card to Steven, who took it warily. Vicki had to pull his arm down to see.

The card was small and white. On it, in very small letters, were the words:

"An invitation to what?" Steven asked.

"An invitation to a mystery," the Doctor replied, frowning and looking away.

Vicki took the card from Steven. "Who gave it to you?" she asked the Doctor.

"I don't... I don't remember," the old man admitted.

"It's a trap," Steven said firmly. Vicki watched with some amusement as he narrowed his eyes, squared his shoulders and generally tried to look heroic.

"Don't be stupid, Steven," she said, and placed the card carefully upon the top of the translucent cylinder in the centre of the control console. "How can it be a trap if it doesn't even tell us where to go?"

With a low hum, the collection of fragile objects in the centre of the translucent column, the things that had always reminded Vicki of a cross between a child's mobile and a butterfly collection, began to revolve around their central axis. The column itself began to rise and fall rhythmically, whilst lights flashed on the console and the deep vibration of the TARDIS in flight slowly spiralled down towards the grinding, clashing noise of landing.

"Well," the Doctor said, "it would appear that someone knows where we are going."

There was a rat on the stairs again.

Carlo Zeno came face to face with it as he rounded the corner. He was standing on the tiny landing that lay between his own rooms on the second floor and his tenant's rooms on the third. The rat was seven steps higher than he was, on a level with his face. Bright afternoon sunlight streamed through the holes in the rotted window shutters, illuminating it: fat and fearless, its black hair matted and its tail coiled like a pink worm. Zeno could even see the avaricious, calculating gleam in its eye.

"Back to the Devil, you garbage-eating fiend," he snarled, and started up the stairs towards it, stamping his boots on the wood. The rat watched for a moment, then calmly turned and scuttled towards a hole in the plaster-covered laths of the wall. As Zeno advanced past the stair, he thought he saw its whiskers twitching in the darkness. God and the Doge alone knew how many rats infested his house. Hundreds perhaps. The scrabbling of their claws kept him awake at night as they ran across the floor, scuttled behind the walls and scrabbled between the joists of the ceiling. Rats were the bane of Venice. Rats and Turks.

The door to the top floor of the house was closed, and Carlo pounded on it. "I've come for the rent!" he shouted, but there was no sound from within. Perhaps his tenant had gone out for a walk, or to buy some food, although Carlo hadn't heard him on the stairs. Perhaps he was asleep. Grimani the barkeeper said that the man drank until he could hardly stand up some nights, and the widow Carpaccio across the alley said she often saw his lamp shining until sunrise. Carlo hadn't asked what the widow Carpaccio was doing awake at that time: it was well known in the district of San Polo that she entertained gentlemen in order to pay her bills. Carlo, on the other hand, was forced to depend on those temporary visitors to Venice who wanted more freedom than that offered by a hotel.

"The rent!" he shouted again, slamming the heel of his hand against the wood. "Do you hear, you lazy slugabed?"

The door was suddenly pulled open. The room was dark, and smelled of sour wine, old fruit and unwashed bedding. The scant light from the window down on the landing barely illuminated the sullen figure of Carlo's tenant. His shirt was undone, and his breeches were creased as if he had been sleeping in them.

"You fat oaf," he said in his haughty Florentine accent. "Unless you've come to tell me that the Doge has finally granted me an audience, or that the lagoon is flooding, I'll have your tongue for a garter."

Carlo stared blankly at his tenant's plump, bearded face for a few moments. He could barely stop himself from picking the man up and throwing him bodily down the stairs. What incredible arrogance! He'd been occupying Carlo's top floor and the roof platform for two weeks now, and Carlo had yet to receive a pleasant word from him. Or any money.

"You think you frighten me with your talk of the Doge?" Carlo snapped. "If you think I'm going to waive the rent you owe me just to curry favour then your brain is addled and your wits have run away."

"You'll get your money when I've got mine," the man said, running a hand through his tousled hair. "The Doge will reward me well for what I can give him."

"If I could spend your promises then I'd be eating peacock tonight. If I don't get the money owing to me by sundown, I'll throw you and your belongings into the canal!"

Carlo turned to go, but a hand descended on his shoulder, stopping him. He turned, ready for an attack, but his tenant had twisted his mouth into what he probably hoped was an ingratiating smile. The expression didn't look at home on his face: the fleshy lips beneath that beard were more suited to a sneer.

"I... please, I apologize for my manner," the man said. "I find myself embarrassed by a temporary shortage of funds, not a position that a gentleman of noble birth and breeding, such as myself, is used to -"

"Not too embarrassed to drink your weight in wine every night," Carlo grumbled, slightly mollified by the man's tone. "Or do you pay Grimani in stories too?"

"- but, as I was about to say, I have just enough left to pay you what I owe." He turned away and disappeared into the gloom of his rooms. He was muttering something beneath his breath: elaborate Florentine curses, no doubt. Carlo heard him rummage among his possessions for a moment, then he was back, appearing suddenly in the slice of light from the landing like a demon on stage. "Here," he said, handing over a small leather bag with obvious reluctance. "It should -" he winced slightly "- suffice, until the Doge pays me for my services."

Carlo weighed the bag in his hand. The coins chinked comfortingly, and he ran through all the things he could do with the money. He'd go and pay his own bill at Grimani's tavern, then perhaps the widow Carpaccio might be willing to accept a few coins in exchange for an hour or two of pleasure.

"That'll do," he said gruffly. "For now. But mind you pay me promptly next week, otherwise I'll have the police call round! He spat to one side, making sure that his tenant knew he didn't believe these stories about audiences with the ruling authority of Venice, then turned and clattered down the stairs. Turning at the landing, he saw the man's eyes gleaming in the dark gap between door and jamb. The thought put him in mind of the rat he had seen earlier. Shivering, he crossed himself and continued round the corner and down, past his own rooms, to the door.

As he walked out into the narrow alley that separated his house from the widow Carpaccio's, he glanced upwards. The lip of the roof platform jutted over the edge of the roof towards a similar platform on the widow's house. He could still remember the way she used to sit up there for hours bleaching her hair in the bright sunlight. That was when she had been young and beautiful, and Carlo had been younger and full of life. He used to watch her from his bedroom window, waiting for the wind off the Adriatic to skim the roofs of the houses and lift her skirts a few inches. Ah, the follies of youth.

He squinted for a moment. Was there something on the platform? Something long and tubular, shrouded in a velvet cloth?

He shook his head. He had coins and Grimani had a new consignment of Bardolino wine from the mainland. By the end of the evening, he hoped that their respective positions would be a little more equitable.

Steven Taylor stood in the TARDIS doorway and looked around. They had landed on a beach of mixed sand and pebbles that fell steeply to a blue sea. A few hundred yards away, a mist hovered over the waves, hiding the horizon and turning the low sun into a dull circle. The mist thinned overhead to reveal a purple sky. Steven couldn't tell whether it was naturally that colour or whether it was a temporary meteorological condition.

He took a cautious sniff of air. It smelt... well, it melt like nothing else he had ever smelt. That was one of the problems about being a space pilot. He'd gone from living in a cramped apartment in the middle of an Earth Hiveblock to living in a cockpit in the middle of deep space, with only the occasional night in a space station to relieve the monotony. Even his time imprisoned on Mechanus had been spent in a small, sterile metal room. The first new thing he had smelt since childhood had been the burning forests during the Dalek attack, and since then he had been plunged from new world to new world, each one of which didn't smell like anything he had ever smelt before. Things always looked like other things he'd seen, things even sounded like things he'd heard, but smells were unique. Individual. Incomparable.

"What can you see?" Vicki asked from behind him. "Oh, get out of the way Steven."

He stepped out of the TARDIS, feeling the sand crunch beneath his boots. It was hot and humid, and he could feel sweat prickle beneath his tunic and across his scalp.

Vicki pushed past him and walked a couple of steps towards the water. "I love oceans," she said cheerfully. "There weren't any on Dido - not within walking distance, anyway, and I used to dream about them."

"Don't touch that liquid, my dear," the Doctor fussed as he left the TARDIS and carefully locked the door behind him. "It might be acid, or... or all manner of things." He slipped the key into his waistcoat pocket, and cast a quick glance at Steven. That key had been the source of several arguments between them. Steven felt that he should have his own key, just in case anything ever happened to the Doctor. The Doctor dismissed the idea, claiming that Steven was just scaremongering. The truth was, of course, that he didn't trust Steven an inch.

The one thing they were both agreed on was that Vicki shouldn't have one.

"What a wonderful place," the Doctor said, gazing around. He sniffed the air in the same way that Steven had seen him sniff fine wines. "Salt marshes, I think you'll find. Ah, yes, and wood smoke. There must be a settlement of some sort nearby." He walked a few steps down the beach and bent down to pick up a dried out strand of seaweed. "No sign of tides," he said, examining it carefully. He moved towards the water's edge. Taking a small strip of paper from a pocket, he bent forward and dipped it in the water. "And the neutral pH indicates that this liquid is safe. You may go paddling if you wish." He turned to find Vicki already standing ankle-deep in the water. She smiled apologetically. He frowned and wagged a finger at her. "Foolish child," he chided. "You might have got yourself into all sorts of trouble, and then where would you be, hmm?"

"Sorry, Doctor." Vicki looked genuinely crestfallen. The Doctor turned to Steven. "Salt water but no tides. What does that suggest to you, my boy?"

"No moon?"

The Doctor nodded judiciously. "Yes, or... ?"

Steven shrugged. "Or a lagoon. Is it important?"

"Most instructive, hmm? A lagoon. Yes." A breeze ruffled the Doctor's long, white hair. Steven stared at him, wondering what the old man was getting at. Sometimes, just sometimes, it occurred to him that the Doctor possessed a laser-sharp intelligence that he chose to hide in vague mutterings and abrupt changes in mood and conversation, but most of the time he just thought that the Doctor was a senile old fool.

"Doctor! Steven!" Vicki's voice cut through his thoughts. He turned, crouching, ready to protect her from whatever threat had sprung from hiding, fight any monster that was lurking in the vicinity, but the beach was empty apart from the three of them and the TARDIS. Vicki was pointing out to sea, into the mist. Or, rather, into where the mist had been. The breeze had thinned it out and shredded it, revealing sketchy details of the waterscape beyond. Near at hand there were islands, some barely more than sandbanks with sparse vegetation, some rocky and covered with bushes. Beyond them, scarcely more than a darker grey shadow against the grey mist, there was a city: a fabulous city of towers and minarets, steeples and domes, all seeming to float upon the water like a mirage.

"Ah," the Doctor said, "just as I thought - we've arrived at Venice."

"Venice?" Steven and Vicki chorused together.

"A city built on sandbanks and wooden pilings, just off the Italian coast. It sank beneath the waves centuries before either of you were born. Well, I rather think I know where we're meant to go, hmm? Vicki, my dear, why don't you go back inside the TARDIS and retrieve the dinghy from the store cupboard by the food machine?"

Vicki nodded and, taking the key which the Doctor proffered, vanished inside the time and space machine. As soon as she was out of earshot, Steven turned to the Doctor. "I don't like this. It smells like a trap to me."

"And to me, dear boy." The Doctor nodded. "A trap, indeed. I am in complete agreement."

"And you're just going to walk into it?" Steven said, aghast.

"Whoever gave me that invitation had me in their power, and let me go," the Doctor mused. "If this is a trap, and it has all of the classic signs, then perhaps we aren't the intended victims."

"No?" Steven frowned. "But if we're not the victims, then what are we?"

The Doctor's bright blue eyes twinkled. "Perhaps we're the bait!"

Galileo Galilei, ex-tutor to Prince Cosimo of Tuscany, Professor of Mathematics at the University of Padua, equal of scholars and natural philosophers and heir to the mantle of Bruno and Brahe, burped and took another swig of wine from the bottle.

Light trickled between the curtains, casting a bruised purple illumination across the strewn clothes, piles of manuscripts and half-eaten plates of food that filled the space in the room. Nearly sunset, then. Nearly time to start work.

That damned landlord had irritated him to the point where he had almost struck the man down. Venice should be paying him to be there, not the other way around. Things would change soon. Oh yes, things would change. All he needed was five minutes with the Doge on top of the bell tower in St Mark's Square, and his fortune would be made. All of Italy - no, all of Europe - would defer to him. The name of Galileo Galilei would resound through the ages.

He staggered across the rotting, creaking floorboards towards the tiny stairway that led upwards, towards the platform on the roof. This place was a death-trap, what with the galloping rot and the rats both competing to see who could gnaw their way through the timbers fastest. One good sneeze could bring the place down around his ears.

Things had been different on his previous visits. He was used to whoring and drinking with Gianfrancesco Sagredo in his palace on the Grand Canal, or debating natural philosophy with Friar Paulo Sarpi in the Doge's Palace. Sagredo was in Syria now, drawing a diplomat's salary and, no doubt, raking commissions off crooked merchants and rapacious pirates. Sarpi, by contrast, was still recovering from the fifteen stab wounds he had suffered during the attempt on his life by agents of the Pope. Galileo had seen the wounds, and was amazed at his old friend's survival. One of the stilettos had entered Sarpi's right ear, passed through his temple, shattered his jaw and exited through his right cheek. Sarpi had claimed that God was smiling on him that day. Galileo couldn't help thinking that if that was God smiling, what must his wrath be like?

He hauled himself up the ladder and on to the platform. The air was cold, and the platform gave slightly beneath his bulk. Just his luck if a strut snapped, sending the greatest philosophical mind in Christendom tumbling into the alley below. Thus did God check the excess pride of man.

He walked to the edge of the platform, past the velvet-shrouded object in the centre and the chair beside it, and gazed out across the city. The sky was the deep purple of grapes, and tinged with fire along one edge where the sun had descended beneath the line of houses. Soon it would be night. The moon had already risen like a plate of burnished pewter sent spinning across the sky. His moon. The object given to him by God for his own personal glory. The flambeaux that burned across the city, illuminating the distant campanile tower with fitful light, mirrored the searing ambition in his heart.

He reached out and tugged the velvet cloth off the shrouded object, throwing it carelessly across the chair. The spyglass beneath - brass half-covered with scarlet cloth - shone in the last few glimmerings of sunlight. About the length of his arm, it sat on a tripod inscribed with calibrations, symbols and Latin inscriptions. He had constructed it in his own workshop in Padua, based on what his friends and his spies had heard of Hans Lipper-shey's work in Germany, but he wouldn't be telling the Doge that. No, as far as the Venetian nobles were concerned, he had invented the whole thing himself. What to look at? He could turn it North, towards the Italian coast, and onwards towards Padua and beautiful Marina. Or he could turn it South, gazing out into the Adriatic Sea and the incoming fishing boats.

He smiled to himself. Marina would be asleep and the fishing boats would wait. No, there was only one choice. He swivelled the spyglass upwards and aligned it roughly towards the silvery disc of the moon. By eye he could make out the mysterious shapes that lay across its surface like veils, but with the spyglass he could make out rough circles and lines that changed their appearance as the sun moved in relation to them and its rays struck them at different angles. Nobody else had seen what he was seeing! The knowledge almost made him drunk with delight.

He removed the leather cap from the glass lens and sat down in the chair. Leaning forward, he gazed through the glass. Perhaps tonight God would inspire him to discover what these shapes were, and why they changed.

The moon's surface was startlingly white - bone white - with fuzzy grey shapes marring its perfection. Galileo forgot the cold, and forgot the uncomfortable position that he had to adopt, as his eye scanned the surface, looking for -

He jerked back suddenly, almost upsetting his chair. That couldn't be right. Surely not. He bent down and gazed through the lens again, then blinked a couple of times. Perhaps what he had seen was a mote in his eye, or a bird passing across his field of view. He looked again. It was still there: an object, too small to recognize but too large to ignore. Its shape was circular, like a discus, and it spun rapidly while moving in a straight line. It was moving at an angle, but there was no doubt that it was heading away from the surface of the moon and towards him.