Nikki's beliefs are put to the test as she realises they are facing murders that are committed for sheer pleasure.

The team is drawn into the investigation of a series of brutal, apparently motiveless murders in the academic world.

A paranoid schizophrenic goes on a violent frenzy in a busy high street. When a young man from the same care home commits suicide, Nikki is convinced there is a connection.

Harry discovers Nazim's death may not have been suicide. Is Dr Sanders the culprit? Meanwhile Leo investigates the murder of a bank manager.

When his wife and teenage daughter are involved in a hit-and-run car crash, Leo begins a painful journey back to his native Sheffield.

As the police infiltrate a gang of identity thieves, Leo faces a choice between justice and revenge.

The team is called to a drive-by shooting outside a London nightclub. They arrive to a scene of carnage with several people dead, or dying.

The man behind the bloodshed pits both factions against one another and the team are in a race against time.