Gary McKinnon doesn't smoke dope anymore. It used to be a part of his life, a shortcut to calm on those long nights he spent perched at his computer, escaping his boredom and exploring the universe. But those nights brought him to where he is today, so he gave up weed without hesitation. "Wouldn't you?" he says, a sardonic smile creeping across his angular face. It's late morning on a winter day, and McKinnon sits at his table in the Bird in Hand, a pub in a far reach of North London, biding his time in legal limbo.

The man whom former U.S. attorney Paul McNulty has accused of having orchestrated "the biggest military hack of all time" isn't sure how long he'll remain out of prison. He's also not sure what harm he's done to the United States. (Nor, apparently, is the United States.) But McKinnon, unnoticed by the handful of serious drinkers bothering the barmaid, is alert and intelligent, and his voice quietly carries an unblinking certainty. Especially when he speaks about the great loves of his life: science fiction and UFOs.

It wasn't so long ago that the 40-year-old Scotsman was a teenage boy migrating to London with his family or, after that, a working stiff with dreams of becoming an actor. There's certainly a soulfulness behind his sharp, Bowie-esque features, but he's landed just one onscreen role, in a small British sci-fi film called Lunar Girl. In his twenties and thirties, he parlayed a childhood interest in computers into a career as a systems administrator. At night, he would get stoned and surf online, trying to satisfy his long-standing curiosity about UFOs. Eventually, his thirst for proof of other worlds would bring about his downfall.

Soon—no one knows exactly when—McKinnon's fate will be determined by the Court of Appeal. He's within one flick of extradition to the U.S., where he faces up to 60 years in prison, or perhaps indefinite detention in Guantanamo Bay, Cuba. Prosecutors call McKinnon a ruthless hacker who wreaked havoc on America's most vital defense systems. McKinnon's legal team and human-rights activists deny such claims and offer dark interpretations of the prosecution: They say that McKinnon's a harmless, self-described "bumbling computer nerd" who inadvertently shamed the U.S. by effortlessly penetrating its post-9/11 government networks—and that the embarrassed superpower is making an example of him for wayward hackers everywhere.

McKinnon was arrested for hacking in Britain in March 2002 and indicted by the U.S. that November. Under the U.K.'s Computer Misuse Act, he'd be looking at a few years in prison, says his lawyer, Karen Todner. But unfortunately for him, Britain and the U.S. enacted a treaty in January 2004 that permits the U.S. to push for his extradition without having to present a case against him. In fact, Britain's National Hi-Tech Crime Unit (NHTCU), which initially arrested him, says it was told to "de-arrest" him, clearing a path to a potential U.S. prison term that could last the rest of his life.