The story takes places in 1972 and the head of MI5 (Brian Cox) sets up a secret committee that includes interrogator Joe Lambe (Tom Hughes), Bobby Waterhouse (Paul Ritter), detective Jim Fenchurch (Shaun Dooley) and secretary Wendy Straw (Chloe Pirrie), Sarah Montag (Victoria Hamilton), and her husband Alan (Jonathan Aris), to locate sleeper agents for the Soviets in this six-part British miniseries written by Toby Whithouse.