Dorian plays Det Superintendent Colin Foster, who is working on a series of murders directed at pathologist Sam Ryan (Amanda Burton).

Professor Sam Ryan is preparing for a high profile case at the Old Bailey. While giving evidence Sam recognises Jayne Rooke in the public gallery and the distraction causes her to make a simple mistake. At home, Rooke (Annabelle Apsion) updates a scrapbook with images and press cuttings of Sam.

A driving school car parks in a car park; a motionless body sits in the passenger seat stabbed to death. The driver cuts open the victim's shirt and takes a photograph before fleeing. Harry (Tom Ward) joins Det. Superintendent Colin Foster (Dorian Healy) at the scene. The victim is Mr Miller, a driving instructor from Cambridge, teaching a Mr Ray Mans. Harry suspects Mr Miller was murdered in Cambridge and then driven to London to be found. Then Harry attends a mysterious case in which Josie Grey is found dead in her bath. Elsewhere, Paul Bearman is shot dead outside his house.

Later, Sam receives photographs of Miller and Grey along with Bearman and recognises him. She compares the various images that have been sent to her and determines that they are all 'textbook murders' inspired by photos from a book of forensic pathology and all have a connection with Cambridge. Metcalf also establishes that Ray Mans is an anagram of Sam Ryan and Cambridge is where Sam trained as a pathologist. When Sam arrives home a trunk is waiting outside her house. Opened, it reveals a headless body. Minutes later Sam receives a text message suggesting that she is next...