Silent Witness originally followed the work of forensic pathologist Dr. Sam Ryan, played by Amanda Burton. In 2004, Burton left the series and Nikki Alexander, played by Emilia Fox, joined Dr. Leo Dalton (William Gaminara) and Dr. Harry Cunningham (Tom Ward) on the forensic pathology team. The series was created by an ex-police officer, Nigel McCrery. Jack is rushed to hospital after collapsing at the scene of a car crash. Thomas discovers that soldier John Sealy may have been exposed to a nerve agent. Thomas investigates the case of John Sealy, a soldier who died during a military training exercise involving exposure to CS gas. It appears John died from an aneurysm, but when Thomas discovers the trace of a possible nerve agent in his system, the family are desperate for answers. The Lyell team identify the concrete-encased remains as those of Derek Marshall, survived by his wife Sue and sister Ann. Clarissa traces payments to a cryogenics facility, leading to the discovery of another suspicious death. Lacking any proper documentation, the coroner orders a post-mortem into the cryogenically frozen body. How did they die, and why was the decision made to freeze them? Teenagers messing around in a stolen car collide with a concrete pillar in a multistorey car park. The joyriders escape, but within the smashed concrete, the unmistakable form of a skull is revealed. After painstakingly extracting the skeleton encased inside, Nikki and the Lyell team must investigate a suspicious dating back 20 years. Meanwhile, Clarissa faces a difficult decision regarding her mother’s care. Nikki determines that Jenny must have died before making contact with the tracks. But when the search for Jenny’s killer hits a wall, her friends at the women’s refuge seek answers. Meanwhile, Thomas’s political ambitions lead him to make friends in high places. Offers are made to open all the right doors for Thomas, but what do they want in return?