Plot

When intelligence agent Kathryn Woodhouse is suspected of betraying the nation, her husband - also a legendary agent - faces the ultimate test of whether to be loyal to his marriage, or his country.

British intelligence officer George Woodhouse is given one week by his superior, 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 SIS operatives, over for dinner. The four suspects are satellite imagery specialist Clarissa, her boyfriend and managing agent Freddie, agency psychiatrist Zoe, and her boyfriend and managing agent James. At dinner, George drugs their food to lower their inhibitions. In an effort to learn more about the guests, George engages them in a psychological game. Amongst other things, it is revealed that Freddie has been cheating on Clarissa; in response to which Clarissa angrily stabs Freddie in the hand with a steak knife. That same evening, Meacham dies of a suspicious heart attack while drinking in his home. George becomes suspicious of Kathryn after finding a theatre ticket in his dresser waste basket yet she denies having seen the film. He breaks into her office and learns she will be traveling to Zurich. He persuades Clarissa to redirect a spy satellite and watches Kathryn meet with a Russian operative in Switzerland. Meanwhile, James informs George that Kathryn has access to a Zurich bank account containing £7 million in misdirected and unexplained funds. In a tense psychiatric session, Zoe asks if Kathryn prioritizes her career or her husband. In a subsequent session, Zoe breaks up with James. Freddie informs Kathryn that George suspects her. It is revealed that during the few minutes George redirected the satellite to watch Kathryn's meet in Zurich, another Russian operative disappeared from a Liechtenstein safe house with a copy of the Severus program, and he is now en route to Eastern Europe to use it to cause a nuclear meltdown. Kathryn uses Clarissa to track the Russian. She suspects that their boss, Stieglitz, deliberately allowed Severus to leak in order to cause a nuclear meltdown and destabilize the government even though it may kill thousands of innocent people. She leaks the Russian's location to a CIA contact, resulting in a drone strike killing both Russians in Poland. George puts all suspects except Kathryn through a polygraph to determine when they first learned about Severus. In bed that night, husband and wife compare notes and realize they are being set up. They invite the other four suspects to a second dinner party. Instead of serving dinner, Kathryn places a gun on the table while George says they will play a game. He reveals several secrets; namely, that Freddie and Zoe had an affair, and that Zoe learned of the Severus program from James but attempted to stop its dissemination due to her Catholic faith. George states that there were two plots: one by Stieglitz and James to leak Severus and cause a nuclear meltdown, and another by Zoe and Freddie to use Kathryn to stop it. James grabs the gun, confesses to plotting with Stieglitz and killing Meacham, and then aims the gun at George and fires twice. However, the gun was loaded with blanks. Kathryn pulls a gun from her bag and shoots James dead, after which she firmly warns the remaining colleagues to never exploit her and George's mutual fidelity again. The remaining colleagues dump James's body in a pond and return to work. Kathryn informs Stieglitz that his plot failed and suggests he remove himself from the picture. She and George reaffirm their love for each other. At Kathryn's questioning, it is revealed that the Zurich bank account containing £7 million is still untouched.