Law & Order: UK

A car is left on a railway level crossing causing a catastrophic train crash which kills fifteen people, though the car driver cannot be found. DS Sam Casey struggles to cope after failing to save a young boy at the scene of the incident. This forces DS Ronnie Brooks and the recently promoted Wes Leyton, who is an old colleague of Ronnies and who is covering for DI Natalie Chandler, to keep a close eye on him. Initially the police suspect the car owner, the unpleasant Michael Gennis (Adam James), but learn that the car was stolen and the actual driver, Finn Tyler (Aidan McArdle), intended to kill himself by driving onto the track but changed his mind at the last minute.