What makes Cooper so tantalizing and popular a topic (Skyjack’s bibliography features three full-length books about the case) is that when he parachuted out of Northwest Oriental Airline’s Flight 305, he—and $200,000—disappeared without a trace. And though Gray doesn’t solve the case, his years of research turned up a cast of characters living on the fringe, all of whom are slightly desperate to prove that someone they know was Cooper.

There’s Barbara Dayton, née Robert, a transsexual with a startlingly thorough knowledge of the speeds and altitudes involved in the jump. Or was it former Northwest Oriental Airlines purser Kenneth Christiansen? Or maybe the mysterious Duane Weber, whose widow spends decades of her life researching his criminal past and whose shady history leads Gray down a rabbit hole of possible government conspiracies? The possible suspects are endless and the law enforcement agents assigned to the case over the years are obsessed. By the time Skyjack ends, Gray himself—isolated in a cabin, hiding at the sound of footsteps outside—is more than a little obsessed himself.

If the narrative dead-ends (a given, since the case remains unsolved), it’s Gray’s meticulous, New Journalism pursuit of all possible leads that eventually drives the story. He combs through yearbooks; he goes searching in the woods where Cooper was assumed to have landed. He starts seeing clues in everything, even a cherry cheesecake recipe. After a while, the central mystery takes a backseat to the mysteries surrounding the men and women still obsessed with Cooper, like whether a famed civilian Cooper sleuth is actually as dedicated as he says, or if Weber’s widow has been reduced to sheer paranoia for no reason. There’s no destination in sight, but Skyjack is one hell of a ride.