Department S S01E17 - The Last Train to Redbridge

When the tube pulls into the final station, a conductor discovers an entire car full of dead people. They turn out to have been poisoned with nerve gas. The question is why, and the case is handed over to the Department.

A first clue - as well as further complication - comes when Annabelle is at the morgue with one of the victim's wife and the woman is abducted at gunpoint... Meanwhile Jason, on the trail of a suspect, is also overpowered and abducted, and soon he and the woman find themselves locked up together in the same underground place. Stewart and Annabelle, the latter posing as a new secretary at a firm they suspect to be involved in the crime, are trying to locate them. Then her new 'boss' at the firm gets suspicious of Annabelle and she disappears, too... while Jason turns up in a hospital, having been exposed to nerve gas and lost all memory of what happened or where he's been... so Stewart has his hands full trying to get him to remember anything that can help lead them to Annabelle and the gangsters...