Former MI5 agent Harry Tate is drawn back into the field when an old friend goes missing - and discovers the stakes could not be higher. Harry Tate has one rule: you don't abandon your friends. When he learns that former colleague Rik Ferris has had a breakdown and disappeared, allegedly in possession of highly sensitive secrets from MI6's archives, he agrees to look for him and, if possible, bring him back in. But where to begin?...