Thomas investigates the case of John Sealy, a soldier who died during a military training exercise involving exposure to CS gas. It appears the victim died from an aneurysm, but when Thomas discovers the trace of a possible nerve agent in his system, the man's family are desperate for answers. Was a chemical weapon involved, or is there a more innocent explanation? Feature-length instalment of the crime drama, starring Emilia Fox, David Caves, Richard Lintern and Liz Carr