Tom Hughes stars as an MI5 spy in this six-part drama series set during the Cold War. MI5 chief Daddy (Brian Cox) assembles a secret committee of intelligence officers to investigate a Soviet plot after one of his Russian informants is recruited to take part in Operation Glass. Not knowing who to trust and with the threat of nuclear war hanging over them, the team made up of interrogator Joe Lambe (Hughes), civil servant Bobby Waterhouse (Paul Ritter), agents Sarah (Victoria Hamilton) and Alan Montag (Jonathan Aris), detective Jim Fenchurch (Shaun Dooley) and secretary Wendy Straw (Chloe Pirrie) race to discover the true nature of the covert plot. But the secret group soon discover they have a mole operating amongst their number...