Detective Everett Larkin of New York City's Cold Case Squad has been on medical leave since catching the serial killer responsible for what the media has dubbed the "Death Mask Murders." But Larkin hasn't forgotten that another memento-another death-is waiting to be found.

Summer brings the grisly discovery of human remains in the subway system, but the clues point to one of Larkin's already-open cases, so he resumes active duty. And when a postmortem photograph, akin to those taken during the Victorian Era, is located at the scene, Larkin requests aid from the most qualified man he knows: Detective Ira Doyle of the Forensic Artists Unit.

An unsolved case that suffered from tunnel vision, as well as the deconstruction of death portraits, leads Larkin and Doyle down a rabbit hole more complex than the tunnels beneath Manhattan. And if this investigation isn't enough, both are struggling with how to address the growing intimacy between them. Because sometimes, love is more grave than murder.