Your next-door neighbor disappears. There’s no reason for her to have gone missing, but gone she is, and long enough to be forgotten. Then suddenly, decades later, she returns, now with a child or two and a strange look in her eye.

If these events took place out in the American desert, you might chalk them up to UFOs. If your neighbor lived on the coast of Japan, however, then it would not be unreasonable for you to attribute the disappearance to North Korean spies—for, in the late 1970s, those spies were indeed landing in Japan, kidnapping unsuspecting men and women and even children, and spiriting them off to the glorious fatherland of Kim Il-Sung and Jong-Il, there to be turned into spies themselves and agents of revolution.

This odd history, scarcely known to many Japanese, is the subject of journalist Robert Boynton’s new book The Invitation-Only Zone, its title referring to the ironically named sectors of North Korea where these foreign “guests” were settled. One was a 20-year-old collegiate named Kaoru Hasuike, who, along with his girlfriend, Yukiko Okudo, was taken from a beach on a summer night, bound and gagged, loaded onto an inflatable raft, and transferred to a North Korean ship offshore. From there, they were separated for months, isolated and “reeducated,” then finally reunited in their unwanted new homeland. Filled with propaganda about the glories of the Kim dynasty and the need to bring the world’s oppressed proletariat to the North Korean way of thinking, they lived in that invitation-only zone until, in the end, no one could figure out what to do with them, at which point they were reluctantly returned home in return for the foreign-aid equivalent of a ransom.

Why were these Japanese kidnapped in the first place? “That’s the question,” says Boynton, who teaches journalism at New York University. “I’ve been working on it for years, ever since I stumbled on a story about the kidnappings not long after 9/11. I was disheartened about world events, but this revived my interest. It was full of amazing question marks. Who were these people? What were their lives like while they were there? What were their lives going to be like now that they had returned, having lived, some of them, for more years in North Korea than they had in Japan? It was a story that planted a thousand questions, and our news coverage didn’t really answer any of them.”

For the next dozen years, then, Boynton traveled frequently to Japan and South Korea, gathering information about people whom he calls “perfectly ordinary middle-class people, but who had been put through something very few other Japanese had ever experienced.” Where the official count of kidnappings is only 17, he thinks the number is much higher, perhaps in the low hundreds—a matter on which he’s met much resistance from all official parties concerned, who, Boynton says, “were hoping I’d be satisfied with their prepackaged version of events.”

He wasn’t, and his story takes many odd twists as a result. Of a piece with Paul Fischer’s book A Kim Jong-Il Production, which concerns a similar (and apparently ongoing) North Korean campaign to kidnap South Koreans, The Invitation-Only Zone seems at points scarcely believable. Bound up in a long history of enmity and friction, it is an imaginative, literate investigation of a strange kind of social engineering that wrecked untold lives—and that, even after Boynton has brought it to light, still seems very mysterious.