An undercover MI5 agent has gone missing. It's up to Julian Mercer and his team to perform the recovery. There's just one problem. They don't know if the agent has been compromised or if he switched sides.

Agent Owen Shepherd was tasked with infiltrating an IRA terrorist faction. He's been in deep cover for two years, but now that an attack is imminent, he's vanished. While searching for Shepherd, Mercer stumbles upon the terrorist's plans. Mercer's new primary objective - stop the terrorist attack. His secondary objective - find Owen Shepherd.

In order to thwart the attack, Mercer will have to step into Shepherd's shoes to find out exactly what the faction leader has planned and how to stop it. But Julian's growing distrust of the Security Service makes him question everything, from the operation runner's loyalties to the real reason the missing agent went missing. Did the terrorists silence Shepherd or did his own people turn against him?