A train from Glasgow to London is ‘hacked’ and suddenly finds itself on an uncertain journey to an even less certain destination. Joe Roag, a police officer on duty, is a passenger on the train, along with Abby Aysgarth, the acting technical director of the National Cyber Security Centre (NCSC). To stop the train, they must find out who exactly is behind this. But are they up against a hostile state, a terrorist organisation or organised crime?