Six guests share a deadly secret.

One woman is about to uncover it.

Archivist Mara makes her living finding what is lost and noticing what others overlook. When she is summoned to the isolated Blackwood House during a torrential storm, she expects a straightforward job. Instead, she finds a wealthy, secretive ensemble bound together by a twenty-five-year-old lie.

Then the mansion’s grandfather clock, frozen at 11:17, suddenly begins to tick backward, revealing a hidden message. Before the night is over, a guest is found murdered inside a locked room.

Trapped with a killer, Mara realizes the only way to survive is to untangle the truth about what happened on 17 September 2001, and the mysterious identity of the seventh child. But the deadliest secret of all might be buried inside her own fractured memory.