When a strange diary written by what seems to be a tormented, terrified child turns up in a bar in Idaho, detailing the grisly atrocities committed by the diarist's 'master', Special Agent Sylvester Walker thinks he may finally have a lead on his killer. The diary also brings in Tristan Lau, Walker's colleague with benefits and a man with a stubborn case of his own.

As their cases prove connected in ways they never could have anticipated, Walker finds himself guiding Lau through a secret world of magic even as their own connection deepens.