In Gotham City, where heinous acts of violence are a daily occurrence, the GCPD relies on Harley Quinn, a young forensic psychiatrist and profiler, to consult on their toughest cases. But Harley is haunted by one case in particular--when she found herself at the centre of a horrifying crime scene the night she discovered the body of her roommate, left with the signature of a notorious serial killer--The Joker. Years later, when a series of gruesome displays of murder appear throughout the city, the past and present collide as Harley's obsession with finding the depraved psychopath responsible leads her down a dangerous path. She must decide how far she is willing to go, and what lines she is willing to cross, to solve these cases once and for all. Collects Joker/Harley: Criminal Sanity #1-8 and the one-shot Joker/Harley: Criminal Sanity-Secret Files.