The team find unexpected connections between the death of a former US ambassador in a plane crash and the apparent suicide of a successful businessman.

The team discover a connection between the plane crash and a sinister online forum. Meanwhile, Matt is grieving for his friend, putting his relationship with Nikki under strain.

When the body of a missing teenager is found in a field near his village, Nikki and the Lyell team must determine whether the killer is a stranger or a local.

A woman's body is found on railway tracks in London. When the post-mortem reveals signs of domestic violence, it brings back troubling memories for Nikki.

When the team's search for Jenny's killer hits a wall, her friends at the women's refuge seek answers. Meanwhile, Thomas makes some friends in high places.

When a skeleton is found in concrete, the Lyell team must investigate a suspicious death dating back 20 years.

The team's investigation leads them to a mysterious cryogenics facility and the discovery of another suspicious death.

Thomas performs a post-mortem on a soldier who died in military training. His investigation takes a turn when he discovers traces of a possible nerve agent.

Jack is rushed to hospital after collapsing at the scene of a car crash. As he fights for his life, the team must identify the poison to save their friend.