When Joe (Joe Cole), an off-duty police officer travelling on the Glasgow to London sleeper train, realises that someone is attempting to gain control and drive it remotely, he calls Abby (Alexandra Roach), Acting Technical Director of the National Cyber Security Centre for help. However, with the entire UK rail network also under attack, the pair realise that if they fail to get everyone off the Heart of Britain on time, all their lives may be on the line.