A loosely organised Christian movement has spread the word around the globe that Jesus Christ will return to Earth tomorrow to gather the faithful into heaven.
While the Christian mainstream isn't buying the theory, many sceptics are milking it.
A Facebook page titled "Post rapture looting" offers this invitation: "When everyone is gone and god's not looking, we need to pick up some sweet stereo equipment and maybe some new furniture for the mansion we're going to squat in."
The prediction is mocked in the comic strip Doonesbury and has inspired "rapture parties" to celebrate what hosts expect will be the failure of the world to come to an end.
In the Army town of Fayetteville, North Carolina, the local chapter of the American Humanist Association has turned the event into a two-day extravaganza, with a Saturday night party followed by a day-after concert.
"It's not meant to be insulting, but come on," said organiser Geri Weaver. "Christians are openly scoffing at this."
The prediction originates with Harold Camping, an 89-year-old retired civil engineer from Oakland, California, who founded Family Radio Worldwide, an independent ministry that has broadcast his prediction around the world.
The Rapture - the belief that Christ will bring the faithful into paradise prior to a period of tribulation on Earth that precedes the end of time - is a relatively new notion compared to Christianity itself, and most Christians don't believe in it. Even believers rarely attempt to set a date for the event.
Mr Camping's prophecy comes from numerological calculations based on his reading of the Bible, and he says global events like the 1948 founding of Israel confirm his sums.
He has been derided for an earlier apocalyptic prediction in 1994, but his followers say that merely referred to the end of "the church age", a time when human beings in Christian churches could be saved. Now, they say, only those outside what they regard as irredeemably corrupt churches can expect to ascend to heaven.
Mr Camping is not hedging this time: "Beyond the shadow of a doubt, May 21 will be the date of the Rapture and the day of judgment," he said in January.
Such predictions are nothing new, but Mr Camping's latest has been publicised with exceptional vigour - not just by Family Radio but through like-minded groups. They have spread the word using radio, satellite TV, daily website updates, billboards and subway ads from Latin America to Asia.
"These kinds of prophecies are constantly going on at a low level, and every once in a while one of them gets traction," said Richard Landes, a Boston University history professor who has studied such beliefs for more than 20 years.
The prediction has been publicised in almost every country, said Chris McCann, who works with eBible Fellowship, one of the groups spreading the message. "The only countries I don't feel too good about are the 'stans' - you know, Afghanistan, Uzbekistan, those countries in Central Asia," he said.
Mr McCann plans to spend Saturday with his family, reading the Bible and praying. His fellowship met for the last time on Monday.
"We had a final lunch and everyone said goodbye," he said. "We don't actually know who's saved and who isn't, but we won't gather as a fellowship again."
In Vietnam, the prophecy has led to unrest involving thousands of members of the Hmong ethnic minority who gathered near the border with Laos earlier this month to await the May 21 event. The government, which has a long history of mistrust with ethnic hill tribes like the Hmong, arrested a number of "extremists" and dispersed a crowd of about 5,000.
No such signs of turmoil are apparent in the US, though many mainstream Christians aren't happy with the attention the prediction is getting. They reject the notion that a date for the end times can be calculated, if not the doctrine of the Rapture itself.
No one will know for sure whether Mr Camping's prediction is correct until Sunday morning dawns, or fails to dawn.