George Woodhouse, a counterintelligence officer with the National Cyber Security Centre, is given one week by his superior, Philip Meacham, to investigate the leak of a top-secret software program code-named Severus. One of five suspects is his wife, Kathryn, who is also an intelligence officer. He invites the other four suspects, also NCSC operatives, over for dinner. The four suspects are satellite imagery specialist Clarissa, her boyfriend and case officer Freddie, counterintelligence officer James and his girlfriend Zoe, who is also the staff psychiatrist. At dinner, George drugs their food to lower their inhibitions. In an effort to learn more about his guests, George engages them in a psychological game. Amongst other things, it is revealed that Freddie has been cheating on Clarissa, to which Clarissa responds by stabbing Freddie in the hand with a steak knife.