When Detective Kat Donovan matches on a dating app with the fiancé who disappeared years before, she learns that some secrets are best left in the past.

Emma has a wonderful husband and two kids in the suburbs of New Jersey. She also has a secret life as an assassin for hire, a secret that her husband Dave discovers when the couple decide to spice up their marriage with a little role play.

A Philadelphia detective slowly unravels as he nurses a lifelong obsession with an enigmatic female serial killer whose crimes defy explanation.