On Thursday, the Ruby Princess cruise ship docked in Sydney with dozens of undiagnosed coronavirus cases onboard.
Almost 2,700 passengers - some coughing and spluttering - were allowed to leave the ship at Sydney Harbour, catching trains, buses and even overseas flights to get home.
More than 130 people from the cruise have now tested positive, making it the biggest single source of infections in Australia. One passenger died in hospital on Tuesday.
The saga has caused much anger: why was the ship allowed to dock and unload people?
What passengers were told
Passengers have vented their anger over how the situation was handled by ship operator Princess Cruises and Australian authorities.
Elisa McCafferty, an Australian woman who flew home to London with her husband immediately after disembarking, told the BBC: "Nothing was said at anytime about anyone being sick onboard. It was a distinct lack of information coming through from Princess the entire time."
She only learned of the danger while collecting her bags at Heathrow Airport.
"I turned on my phone and I started getting all these notifications from people back in Australia saying 'there's been confirmed cases on the Ruby,'" she said.
"And I was just absolutely petrified. We had just been on two full flights - what if we had infected someone?"
She said she now had a dry cough, fever, body aches and fatigue - and they were self-isolating at home. They were also concerned about their elderly parents and friends who were on the trip too.
Other passengers recalled coming into contact with sick people on the boat and said there were no warnings.
"I think that they let us down," said Bill Beerens, a Sydney man who tested positive for the virus in hospital on the day he disembarked.
"I do honestly believe that they [cruise ship management] knew what was going on and they just wanted us off the boat," he told the Australian Broadcasting Corporation.
Elderly couple Rona and Michael Doubrin said they had symptoms towards the end of the cruise but had not been concerned, because they had not been told to practice social distancing.
"People were going down to the pool, we were lying in the sun, eating in the dining room, dancing, seeing shows," Ms Doubrin told Daily Mail Australia.
"We would have isolated ourselves in the cabin if we'd known. We're not spring chickens - we're high risk."
What happened in Sydney?
After an 11-day voyage, the ship returned to the city before dawn, cutting short its final New Zealand leg as the nation announced a travel ban.
At the time, according to NSW Health, about a dozen passengers reported feeling unwell and they had swabs taken for Covid-19. An ambulance took a passenger to hospital. (The woman, aged in her 70s, died on Tuesday, authorities said.)
But other passengers on board weren't told of this. Instead, thousands streamed off the boat at Circular Quay, just across from the Sydney Opera House. The bustling area leads directly into the city centre, with transit links to the airport and outer suburbs.
Five days earlier, Australia began ordering anyone returning from overseas to self-isolate for 14 days - a directive which applied to the cruise passengers.
But the Ruby Princess passengers weren't screened and were unmonitored when they left the ship. About a third were international passengers - they were told they could travel overseas immediately or self-isolate in Sydney for a fortnight.
"They even said, you can get a train home," said Ms McCafferty.
New South Wales health officials have said they followed national guidelines which allow passengers to disembark if the route is considered "low risk". The Ruby Princess was given that status because it had been to New Zealand only.
One day after the ship docked, officials revealed the first cases of Covid-19 confirmed in three people who had been on board - two passengers and a crew member.
It prompted a scramble to track down everyone else who had been on board.
And at least 21 of the 48 people who had tested positive by Monday were found in other Australian states. By Tuesday, the total number of cases linked to the ship had climbed to 133.
How did this happen?
It is hardly the first cruise ship to see infections - the Diamond Princess, also operated by Princess Cruises, drew global focus in February. Its passengers were quarantined for almost a month off the coast of Japan before being repatriated. More than 600 cases were linked to the ship.
Governments at Australia's state and federal level have pointed blame at each other. Princess Cruises has said it followed official guidelines.
On Saturday, The Australian newspaper reported that the ship had logged 158 ill passengers on its previous voyage to New Zealand. Nine people were tested upon arrival in Sydney on 8 March - and their tests results came back negative. However, two passengers from that journey were found to have tested positive after flying home to Darwin.
NSW port and health authorities declined to reply to BBC questions about these reports.
What have authorities said?
On Monday, Prime Minister Scott Morrison described the mistake as the responsibility of state officials.
NSW Health Minister Brad Hazzard told reporters on Saturday: "With the benefit of what we now know... I'd have said 'yeah, maybe we should hold them on the ship.'"
But he rejected Canberra's accusations that state officials had not properly checked cruise ships upon entry.
"New South Wales is actually going over and above what the national guidelines are," said Mr Hazzard.
State health officials stressed they had run assessments "well beyond federal requirements" for 63 ships which have entered the harbour since mid-February.
Others noted that while Canberra had enacted a ban on cruise ships arriving, it had allowed four including the Ruby Princess to be exempt.
Four other cruise ships into Sydney have been linked to confirmed Covid-19 cases. The Ovation of the Seas ship, which docked in Sydney a day before the Ruby Princess, has seen five positive tests.
Health officials say infected patients are in self-isolation or in hospital. All passengers have been told to quarantine themselves.
In the wake of the Ruby Princess bungle, Western Australia on Monday questioned where it would allow a cruise ship to dock there. The European ship Magnifica is carrying 1,700 passengers - about 250 of whom are reported to have respiratory illnesses.
It was allowed to dock on Tuesday to refuel, but all on board were banned from disembarking.
Premier Mark McGowan had stressed: "I will not allow what happened in Sydney to happen here."