It's a quiet, snowy morning at The Cracked Spine bookshop when book seller Delaney Nichols receives a mysterious visitor, a messenger. He presents her with a perplexing note: an invitation to a meeting with eccentric socialite Shelagh O'Conner, who requests Delaney's participation in an exclusive treasure hunt. Delaney is intrigued, but also cautious: Shelagh, while charming in person, has a reputation for her hijinks as a wealthy young woman in the '70s.

But Delaney is enticed by the grand prize at the end of the treasure hunt: a highly valuable first edition copy of The Strange Case of Dr. Jekyll and Mr. Hyde, by Robert Louis Stevenson. The winner is also to receive the contents of Shelagh's vast library, and all participants will earn a large sum of cash. The night after the first meeting of the treasure hunters, however, several homes in Edinburgh are robbed in a manner reminiscent of Shelagh's old tricks. And when a man connected to Shelagh is killed, suspicion builds. Except Shelagh herself has disappeared from her home, seemingly kidnapped by the villain.

Terror mounts throughout the city as Delaney attempts to solve the mystery, while trying to evade the killer's clutches. But it's hard to know who to trust when around every corner, a new monster could be lurking.