Katherine Schneider's life as a dentist in 1913 New York is upended when a patient reveals details of a deadly plot while under the influence of laughing gas. As she is plunged into danger, she seeks help from the dashing Lieutenant Jonathan Birch, a police officer she has long admired from afar.

Jonathan has harbored powerful feelings toward Katherine for years but never acted on them, knowing his dark history is something she could never abide. Now, with her safety on the line, he works alongside her through the nights as they unravel the criminal conspiracy that threatens her ... even as he keeps his deepest secrets hidden at all costs.