The nine scenes in Betrayal are presented mainly in reverse-chronological order, beginning in 1977 and ending in 1968, although the scenes in the years 1977 and 1973 move forward normally. This summary covers the plot in forward chronological order.
In 1977, a literary agent named Jerry and Emma, the wife of Jerry’s best friend, a publisher named Robert, have their first meeting in two years, in a pub. Their reunion is warm but somewhat stilted. Jerry tells Emma that he spotted her daughter on the street recently. He mentions that he’s heard rumors of Emma’s new affair, with Casey, a writer Jerry and Robert work with, which Emma confirms. Jerry denies being jealous of Casey. Emma reveals that she and Robert are separating, as of the night before: she has just learned that Robert’s had several affairs of his own. Jerry says he never suspected it. Emma tells Jerry she told Robert about their affair last night. Jerry responds with disbelief and disappointment. Emma’s mood is pessimistic.
Later, Robert responds to Jerry’s call, arriving at his house. A tongue-tied Jerry gracelessly laments the fact that Emma has just told Robert about their affair, not seeing why it was necessary. Robert reveals that she in fact told him about it four years ago. Jerry is baffled, barraging Robert with follow-up questions. Robert is typically subdued: he says he doesn’t care about any of this, cynically admitting to beating and cheating on Emma and accepting that his marriage is over. Jerry points out that they’ve continued to meet as friends in the last four years, but Robert counters that they never play squash anymore. They discuss Casey’s declining artistry but concede that his books still sell and make them both money. Jerry says he’s been reading Yeats and reminds Robert of the time he read Yeats on the island Torcello.
In winter of 1975, Jerry and Emma are in their apartment together. It’s been months since they’ve met; Emma has begun running a gallery, and Jerry has had increasing work obligations abroad. They acknowledge that their love has gone cold, and they agree to sell the apartment. Emma angrily departs, leaving her key to the apartment with Jerry.
In 1974, Jerry sits for a drink in Robert and Emma’s living room. He and Robert discuss infant behavior, with Jerry suggesting that male babies feel greater anxiety about facing life. Jerry mentions that he was in their neighborhood because he’d been having tea with the recently divorced Casey. Jerry defends Casey’s latest work, while Robert trashes it for being uninspired and self-indulgent, and Emma calls it “dishonest.” Robert reveals that he's recently been playing squash with Casey, whom he lauds as an opponent. He again presses Jerry on scheduling their next squash match, but Jerry is evasive. After Jerry departs, Robert kisses Emma, who breaks away but then cries softly on his shoulder.
In summer of 1973, Robert and Emma relax in a Venetian hotel room, discussing their planned trip to the island of Torcello. Emma is enjoying a new novel by Spinks. Robert says, to Emma’s apparent surprise, that Jerry represents Spinks and had come to him with the manuscript, but Robert turned it down, feeling that the book’s theme of betrayal is played out. Robert then reveals that a fluke at the Venetian American Express office alerted him to a letter that Jerry sent to Emma. He recalls the long letters about Yeats that he would write to Jerry back in college. Robert didn’t open Jerry’s letter to Emma on principle, but he insinuates that he knows they are having an affair, which she admits. Robert is shocked to learn that the affair has been going on for five years, but Emma reassures him that their one-year-old child is Robert’s.
Later that summer, Emma and Jerry are back in their apartment. Their passion seems as strong as ever. Emma says she couldn’t go to Torcello due to a speedboat strike. She then seems anxious about Jerry meeting Robert for lunch. Emma reveals that Jerry in fact gave her the book by Spinks, whom Jerry characterizes as a solitary eccentric. Jerry reveals that he’s had a few close calls with his wife, Judith, nearly discovering their affair. He then recalls a moment from many years ago that’s been obsessing him, when he, Judith, Emma, Robert, and all their kids were together in his kitchen, and he playfully tossed Emma’s young daughter in the air.
Later that same summer, Jerry and Robert dine at an Italian restaurant in London. Jerry still doesn’t know that Robert knows about the affair. Robert presses Jerry on scheduling their next squash match, but Jerry is evasive. Robert discusses his wonderful trip to Torcello by speedboat, exposing but not explaining Emma’s lie. On the island, he says, he read Yeats at dawn, experiencing a rare moment of true happiness.
Back in 1971, Jerry and Emma’s affair is in full swing. They rendezvous at the secret apartment they’ve rented for the purpose. At this meeting, Emma cooks as she tells Jerry that she saw Judith out at a restaurant with a woman. This prompts a discussion of infidelity—whether Judith knows about their affair, whether she could be cheating on Jerry herself, and finally, whether Emma and Jerry have ever been “unfaithful” to each other, which they both deny. Emma then awkwardly reveals that she’s pregnant with Robert’s child.
Back in 1968, Robert and Emma are hosting a house party. Jerry, drunk, has slipped off to their bedroom where he sits alone. Jerry startles Emma when she enters to fix her hair. Jerry advances on Emma and declares his longstanding, overwhelming love for her. A surprised Emma resists. Robert soon wanders in. Jerry reminds Robert that he was his best man, then continues to praise Emma’s beauty. Robert thinks Jerry is just harmlessly drunk and leaves them be, but once he goes, Emma shows the first sign of yielding to Jerry’s advances.