Shelly Mohan, a housewife and mother of three, makes an irreversible decision, and commits an unspeakable act, when a man from her distant past surfaces - she commits murder.

Shelly's husband Jason, a Garda Detective, is delighted to be assigned to the case, with no sense where the trail may lead. While he and his co-worker, Fiona, focus on a sex worker, Shelly realizes she may have left evidence in the dead man's hotel room.

We learn of Shelly's dark history, as a teenager who was part of a drug ring in London 20 years earlier with Charlie Lynch, the man she shot.  When Lynch's true identity is uncovered, a UK officer, DSI Crichett, reopens an old murder case Shelly and Charlie were linked to.