Jacqui met Bob Lambert at an animal-rights protest in 1984, when she was twenty-two. Their son was born the next year. Two years after that, Bob disappeared from their lives, seemingly without a trace. In this piece for The New Yorker, Lauren Collins investigates who Bob Lambert really was: a British police officer part of a massive undercover operation, whose officers— known as “deep swimmers,”—spent years surveilling different radical groups.