When the Miami Police first found Benito Que, he was slumped on a desolate side street, near the empty spot where he had habitually parked his Ford Explorer. At about the same time, Don C. Wiley mysteriously disappeared. His car, a white rented Mitsubishi Galant, was abandoned on a bridge outside of Memphis, where he had just had a jovial dinner with friends. The following week, Vladimir Pasechnik collapsed in London, apparently of a stroke.  The list would grow to nearly a dozen in the space of four nerve-jangling months. Stabbed in Leesburg, Va. Suffocated in an air-locked lab in Geelong, Australia. Found wedged under a chair, naked from the waist down, in a blood-splattered apartment in Norwich, England. Hit by a car while jogging. Killed in a private plane crash. Shot dead while a pizza delivery man served as a decoy.  What joined these men was their proximity to the world of bioterror and germ warfare. Que, the one who was car-jacked, was a researcher at the University of Miami School of Medicine. Wiley, the most famous, knew as much as anyone about how the immune system responds to attacks from viruses like Ebola. Pasechnik was Russian, and before he defected, he helped the Soviets transform cruise missiles into biological weapons. The chain of deaths -- these three men and eight others like them -- began last fall, back when emergency teams in moonsuits were scouring the Capitol, when postal workers were dying, when news agencies were on high alert and the entire nation was afraid to open its mail.  In more ordinary times, this cluster of deaths might not have been noticed, but these are not ordinary times. Neighbors report neighbors to the F.B.I.; passengers are escorted off planes because they make other passengers nervous; medical journals debate what to publish, for fear the articles will be read by evil eyes. Now we are spooked and startled by stories like these -- all these scientists dying within months of one another, at the precise moment when tiny organisms loom as a gargantuan threat. The stories of these dozen or so deaths started out as a curiosity and were transformed rumor by rumor into the specter of conspiracy as they circulated first on the Internet and then in the mainstream media. What are the odds , after all?  What are the odds, indeed?  For this is not about conspiracy but about coincidence -- unexpected connections that are both riveting and rattling. Much religious faith is based on the idea that almost nothing is coincidence; science is an exercise in eliminating the taint of coincidence; police work is often a feint and parry between those trying to prove coincidence and those trying to prove complicity. Without coincidence, there would be few movies worth watching (''Of all the gin joints in all the towns in all the world, she walks into mine''), and literary plots would come grinding to a disappointing halt. (What if Oedipus had not happened to marry his mother? If Javert had not happened to arrive in the town where Valjean was mayor?)  The true meaning of the word is ''a surprising concurrence of events, perceived as meaningfully related, with no apparent causal connection.'' In other words, pure happenstance. Yet by merely noticing a coincidence, we elevate it to something that transcends its definition as pure chance. We are discomforted by the idea of a random universe. Like Mel Gibson's character Graham Hess in M. Night Shyamalan's new movie ''Signs,'' we want to feel that our lives are governed by a grand plan.  The need is especially strong in an age when paranoia runs rampant. ''Coincidence feels like a loss of control perhaps,'' says John Allen Paulos, a professor of mathematics at Temple University and the author of ''Innumeracy,'' the improbable best seller about how Americans don't understand numbers. Finding a reason or a pattern where none actually exists ''makes it less frightening,'' he says, because events get placed in the realm of the logical. ''Believing in fate, or even conspiracy, can sometimes be more comforting than facing the fact that sometimes things just happen.''  In the past year there has been plenty of conspiracy, of course, but also a lot of things have ''just happened.'' And while our leaders are out there warning us to be vigilant, the statisticians are out there warning that patterns are not always what they seem. We need to be reminded, Paulos and others say, that most of the time patterns that seem stunning to us aren't even there. For instance, although the numbers 9/11 (9 plus 1 plus 1) equal 11, and American Airlines Flight 11 was the first to hit the twin towers, and there were 92 people on board (9 plus 2), and Sept. 11 is the 254th day of the year (2 plus 5 plus 4), and there are 11 letters each in ''Afghanistan,'' ''New York City'' and ''the Pentagon'' (and while we're counting, in George W. Bush), and the World Trade towers themselves took the form of the number 11, this seeming numerical message is not actually a pattern that exists but merely a pattern we have found. (After all, the second flight to hit the towers was United Airlines Flight 175, and the one that hit the Pentagon was American Airlines Flight 77, and the one that crashed in a Pennsylvania field was United Flight 93, and the Pentagon is shaped, well, like a pentagon.)
In paranoid times like these, people see connections where there aren't any. Why the complex science of coincidence is a conspiracy theorist's worst nightmare.