It's the hottest summer on record. The streets are shimmering, walking outside is like walking into a furnace, and yet, someone is still setting fires. Milwaukee homicide detective Ellie MacIntosh is called to an arson scene and finds bewildered home owners, an unidentified corpse, and cryptic clues. Is it a random killing? The ritualistic nature of the crime points to no, and Ellie fears that the already-oppressive summer is just starting to heat up. Ellie doesn't like her obnoxious new partner, Jason Santiago-and he doesn't like her. Yet when she becomes convinced that their investigation is tied to a cold case, Jason finds himself grudgingly starting to agree. It might be hot as hell outside, but the details of the brutal homicide chill him to the bone? .