The overnight train from Glasgow to London is hacked; passengers are trapped on board, including police officer Joe; as the train hurtles towards disaster, Joe manages to make contact with Abby, the cyber security director.

When the cyber attack on the rail network prevents Abby from seeing the obstacles in the sleeper's path, she realises that she's in race against time to avert disaster; with the so-called Driver being one step ahead, she must think fast.

Realising that someone on board may be working with the hackers, Joe turns his attention to his fellow passengers, while Abby stuns her colleagues by taking the train off the mainline.

While Hud's shocking attempt to stop the train his way threatens to end in disaster, Abby is stunned to discover that Joe may be in even more danger than any of them realised.

Joe tries to deal with the fallout from the shock shooting, while deciding whether to put his faith in other passengers; Miller and Hud interrogate Abby.

Abby is convinced that she knows how to stop the remaining carriages; however, with Joe out of contact and time running out, it might be too late for those hurtling towards the end of the line.