S1, E1: Dr. Yvonne Carmichael has a high-flying career, a beautiful home, and the "perfect family." After a confident presentation to a group of MPs, Yvonne is approached by a charismatic stranger, who seems refreshingly interested in what she has to say - interested in her. Before she's had time to stop and think, she finds herself alone and intimate with him in the deserted crypt beneath the House of Commons. Although she never expects to see him again, their encounter builds to an affair, and the unexpected passion that this man arouses in Yvonne shakes her. The affair is made all the more enticing by his enigmatic nature. He gives away very little, and always seems to have one eye cast over his shoulder. He dictates how their relationship plays out, and Yvonne realises that such clandestine planning comes as second nature to him. Is there more to his 'civil service' role than he'll admit? But instead of ringing warning bells, this knowledge only thrills Yvonne even more, despite herself. One evening, dressed up for a colleague's retirement party, she meets her lover beforehand in a bar in central London. Slightly drunk and intoxicated by the thrill of the affair, they end up having sex in a small backstreet alley, Apple Tree Yard. Arriving at the party, Yvonne is glowing. She gets steadily drunk on the free champagne whilst covertly swapping texts with him. But at the end of the night, everything changes for Yvonne. One minute she is buzzing with the passion and excitement of an affair; the next she is devastated and drowning, when violence springs from an unexpected quarter.