A month-long water pistol tournament is under way in the UK. But what makes adults want to "shoot" total strangers in the street?
On a street corner, an assassin waits in silence for his victim.
Dressed all in black, face covered except for his eyes, he looks menacing as he steadies his weapon and prepares to shoot with the cold-blooded eyes of a killer.
But not everything is as it seems. His weapon is bright green and it is water rather than bullets that blasts the hapless, screaming, victim as he fumbles - too late - for his own pistol.
The assassin laughs silently as he lets his soaking-wet prey through the door he was guarding.
He is taking part in StreetWars, a water "assassination" contest that started in London on Monday and which lasts until 29 August.
Kicked off in New York in 2004, the tournament has since visited cities including Vancouver, Vienna, Los Angeles and Paris, and organisers say it attracts between 125 and 300 players. The first London contest took place in 2006 and it returns this month for the first time in three years.
It is a water fight for grown ups where, they say, the entire city is your playground.
However, some city authorities criticise it as "irresponsible" and suggest it might spark security alerts.
The exact rules are kept under wraps, except to those who pay the £40 to sign up.
Players are called to the headquarters of the "Shadow Government" - as the organisers like to be known - to be given details of their target, including home address, work address, phone number and a photo, and then set the task of shooting them in any way they can.
Participants are buzzed through a door and then led to the basement with a gun - well, water pistol - shoved into their back.
Men in trilby hats hand out manila envelopes before players are thrust, disorientated, back into the real world in the knowledge someone with their photo is hunting them down.
Co-creators Franz Aliquo and Liao Yutai have adopted the names of Supreme Commander and Mustache Commander, while the head of the London operation calls herself Eevil Midget.
This eccentricity has spread to participants, with names such as NinjaSquash and Biscuits.
"It's just a bit of fun, but some people do take it incredibly seriously," says Yutai.
"One businessman in San Francisco found his 'mark' was in college. He managed to get into the campus by buying an embroidered shirt worn by staff. After four days the security staff just said hello to him as he walked past - everyone just thought he worked there."
This dedication is not the preserve of Americans.
"The last winner in London stalked his victim all the way to Manchester on the train just so he could shoot him as he left the station," Yutai says.
"He was utterly shocked and at that point you just have to clap your hands and say 'bravo'."
London's first contest was branded irresponsible by British Transport Police who suggested that carrying a water pistol on public transport could constitute a criminal offence, although "kill" attempts on public transport or in stations are banned under StreetWars' rules.
The Metropolitan Police initially suggested this seemingly innocent fun could end up wasting police time by diverting resources from real incidents - though it has softened its position now.
However, New York Mayor Michael Bloomberg's view that the contest is "not funny in this day and age", and that its organisers could "use some psychiatric help", remains unchanged.
StreetWars' backers simply say they are glad of the publicity.
But with British and American soldiers dying on real battlefields, what makes adults indulge in this make-believe?
"The first thing is I'm incredibly competitive but I just think it is a lot of fun," says one participant who did not want to be named - perhaps fearing giving up key information.
"People don't get it until they actually take part. It certainly makes the journey to and from work much more interesting.
"During the competition, I wake up, go to work, leave work then stalk my victim until it's time to sleep."
Another player, Ahmed Murad, says the idea is "just that little bit different".
"What is strange it that it's actually quite difficult. I thought it would be easy but everyone's got their own work and life schedule."
It is not just the prospect of the kill that has caused him some trouble.
"There's an insane amount of paranoia - every time you step out for lunch you are just looking around trying to look everyone in the eye, assuming they are after you."
Many of the players plan journey routes and change them daily, scouts are enlisted to walk ahead and check blind alleyways or dark side-streets and every door is pushed open with the nagging feeling that someone awaits them on the other side.
This thrill of risk makes the game attractive, according to psychologist Dr Martin Hagger, of the University of Nottingham.
"Some do feel like we live in a health and safety conscious society. They feel mollycoddled, so will go for these things. And while they know they're not actually going to die, the element of uncertainty gives them a natural high.
"It appeals to those who are extroverted and have a sensation-seeking personality," says Dr Hagger.
A further lure is the prize. Last player standing takes home a cash sum determined by the number of players, which generally amounts to about £500.
Maybe worth risking a soaking?