Davy, a young boy is drowned in concrete, is it suicide, accident, or murder?

Boyd determines that Esther is the cause of the murder, but who killed her: McDonagh father or son or Killigan father or son?

When a Sudanese leader sews his mouth shut and goes on a hunger strike until the long-missing skull of the Mahdi is returned, the Foreign Office pressures the team to find it.

Boyd connects the disappearance of the Mahdi's skull to the cold case murder of a former Iraqi VIP in his store years earlier and a college-centered Middle Eatern cult.

Demolishing a building in 2007, a wrecking crew discovers two desiccated corpses still conjoined who were shot to death by a single bullet while having sex in 1992.

The relationship of Boyd and Grace becomes strained as he comes closer to the killer and a scenario involving official corruption becomes apparent.

Three murders allegedly committed 20 years earlier because of anger management, are re-examined by the unit when the supposed killer is released from a psychiatric facility.

Another murder has been committed and Boyd knows he must track down the killer before he strikes again. Does the answer lie in events at the children's home many years previously?

A badly decomposed body is discovered buried in a Hampstead garden, while a convicted murderer escapes from a secure psychiatric unit. The team is drawn back to a horrific double patricide from 1967.

After a mental patient slips away after spending forty years for brutally murdering his parents, several leads open up for the cold case team.

When a London flat is being rehabbed a bloody Nazi dagger is discovered in the fireplace and the team joins with a Massad agent in a hunt to solve the case.

When the team begins looking into the Dusnia Family, they find that their DNA does not match.