Anna—who prefers to be called Anastasia—is a spooky and complicated high school girl with a penchant for riddles, Houdini tricks, and ghost stories. She is unlike anyone the narrator has ever known, and they make an unlikely, though happy, pair. Then Anna disappears, leaving behind only a dress near a hole in the frozen river, and a string of unanswered questions. Desperate to find out what happened the narrator begins to reconstruct the past five months. And soon the fragments of curious events, intimate conversations, secrets, letters—and the anonymous messages that continue to arrive—coalesce into haunting and surprising revelations that may implicate friends, relatives, and even Anna herself.