Sam must investigate a case with a painful personal connection when a close friend is murdered after the Cambridge May Ball.

The case becomes entangled in Annabelle's romantic relationships when Sam discovers her friend may have had an affair with a student.

The hunt is on for Mr Harris, but the murderer may be closer to home. Meanwhile, Sam grows closer to surgeon James Reynolds.

A tragic scene is discovered when a young mother apparently dies of an overdose. When another addict dies in an explosion, Sam has a bigger case on her hands.

Are the deaths linked to a drug war or is this the work of vigilantes? Sam suspects a personal tragedy is at the heart of things.

The death of a farmer involving a combine harvester seems like an accident - until Sam receives an anonymous tip-off.

Sam looks for connections between Ian Neal and a killing in Northern Ireland in 1985. Meanwhile DI Connor's wife arrives in Cambridge.