In Melinda’s room, Rosalyn watches her distraught girlfriend pack frantically, demanding that they both flee Cambridge. Melinda keeps repeating that she thought the dead runner was Rosalyn. Rosalyn explains she was sleeping in Melinda’s room because her own staircase was blocked, and she knew nothing about the murder until Melinda’s screams awakened her. She correctly deduces that the victim must be Georgina Higgins-Hart who lives on her floor.

Melinda blames Rosalyn for talking to Gareth about what she witnessed on Robinson Crusoe’s Island, insisting she put both herself and Melinda in danger. In flashback, Rosalyn recalls taking a reluctant Melinda to see Gareth in his office at DeaStu, where they communicated via computer. Gareth appeared grief-stricken, not threatening, and Rosalyn sensed his genuine love for Elena. His reaction sparked unexpected feelings in Rosalyn—jealousy and a sudden desire for a conventional future in place of her volatile relationship with Melinda.

Their argument escalates. Rosalyn refuses to flee, insisting Gareth is not a killer and stating she should have gone to the police immediately as soon as she learned about Elena’s death. Melinda accuses Rosalyn of constantly demanding proof of love and denying her own sexual identity. Rosalyn admits she has never had the chance to discover who she truly is. Melinda gives her an ultimatum: leave together or end the relationship. When Rosalyn declines to leave, Melinda departs, their relationship finished.

The perspective shifts to Lynley and Havers. From a call box, Lynley learns the forensic lab has found no fiber match from Thorsson’s clothing. At the Bliss Tea Room, they discuss the case. Havers remains convinced of Thorsson’s guilt, while Lynley expresses doubts. Catherine Meadows, a young undergraduate, approaches them. She identifies herself as Thorsson’s student and lover, providing an alibi for the morning of Elena’s murder. She insists Thorsson was with her until 6:45. She defends him passionately, claiming Elena fabricated the harassment story after Thorsson rejected her advances. However, when Havers questions her further, Catherine admits Thorsson was not with her the previous night when Georgina was killed. After Catherine leaves, Lynley tells Havers he believes Thorsson is not Elena’s killer. Havers agrees but notes he could still be involved in Georgina’s murder.

Lynley visits Penelope and Harry in Bulstrode Gardens that evening. Penelope has been researching the work of painter James McNeill Whistler and writer John Ruskin, energized by their previous conversation about Sarah’s art. When Harry arrives home, tension surfaces immediately. He criticizes Penelope for reading art books while their baby lies among the laundry, arguing she should focus on her role as wife and mother. Lynley challenges this rebuke, suggesting Penelope should be able to pursue both family and career. Harry insists wives who pursue their own paths destroy families and claims Penelope has everything she needs at home. After Harry leaves for the kitchen, Lynley studies family photographs and realizes that none of them show Penelope alone, only in relation to others.

Later, Lynley and Lady Helen attend a jazz concert at Trinity Hall’s junior combination room. Miranda performs on the trumpet with her combo. During a break, Lynley questions Miranda about Elena. Miranda reveals she suspected Elena was pregnant based on observing morning sickness and noticing Elena had stopped eating her usual breakfast cereal. She says Elena did not seem worried about the pregnancy.

In the adjacent bar, students play darts. One player calls out to challenge a senior member nicknamed Trout. Hearing the nickname, Lynley mentally links the name to the fish symbol Elena repeatedly drew in her calendar. He recognizes a potential breakthrough in identifying Elena’s secret relationship.

Lynley and Lady Helen find the man nicknamed “Trout”—Victor Troughton, a history don at Trinity Hall, in the college bar. Troughton agrees to speak privately and takes them to his rooms. Without prompting, he acknowledges that he knows they have come about Elena and admits he has been expecting them. He confirms that Elena’s fish symbol represented him.

Troughton confesses he was Elena’s lover. He explains that three years earlier, he had become dissatisfied with his marriage to his wife, Rowena, who had gained weight and lost her figure after bearing three sons. He sought young women for affairs but found himself repeatedly rejected until Elena approached him during the Christmas term. She seduced him deliberately, and they began meeting regularly. Troughton fell deeply in love with her, though he recognized she was using him primarily to hurt her father, Anthony, a friend and colleague of Troughton’s. When Elena told him she was pregnant, Troughton agreed to marry her despite knowing the child could not be his due to his vasectomy three years prior. He never told Elena about the procedure. He explains he was willing to pose as the father because he loved Elena and believed his love could eventually heal her anger toward her father. He has no idea who actually fathered Elena’s child but suspects she slept with that man for the same reason she slept with him—revenge against Anthony.

Troughton admits he last saw Elena on Sunday night in his rooms. She left just before one in the morning. He has no alibi for the Monday morning when she was killed.

Afterward, on a terrace overlooking the River Cam, Lynley reflects on the interview. He confesses to Helen that listening to Troughton made him realize how men often want women as extensions of themselves rather than as independent individuals. He acknowledges the ways his own desires follow this pattern. Helen questions whether he could let her go if they slept together once. Lynley says Helen will not marry him because he is not an emotional dependent she needs to save, unlike other men in her life. Their conversation grows intense as Lynley grapples with the ways his desires mirror Troughton’s self-centered wanting. Helen assures him he is not alone in wanting, offering absolution. Lynley tells her to stay in Cambridge and return to London when she’s ready.

Thursday morning arrives with heavy fog. Havers arrives late, worn out from caring for her mother. She and Lynley discuss her impossible situation, with Lynley arguing she holds the power to make decisions about her mother’s care.

They drive to Queens’ College through the fog to interview Gareth. In his room, Gareth communicates via computer. He admits he and Elena had sex once, in London before term began, in her mother’s kitchen. He believed it meant they had a future together, but when he tried to discuss their relationship during Michaelmas term, Elena laughed and dismissed their encounter as meaningless. She told him she was involved with someone else. Devastated, Gareth followed her from St. Stephen’s to Trinity Hall on Sunday night and waited until she emerged just before one in the morning. He confronted her angrily in the street, then left. He denies killing her and has no alibi for either Monday morning or Wednesday morning when Georgina was killed. Lynley and Havers take his boxing gloves for forensic testing.

Outside, Havers argues Gareth has motive, means, and opportunity. Lynley counters that Gareth’s deafness makes him an unlikely shooter—he would have needed to hear Georgina’s approach in the dark countryside to time the shot. As they discuss the possibilities, Rosalyn approaches them. She explains she was running along the river Monday morning, around 6:30, and passed Crusoe’s Island. She believes she saw Elena’s killer.

The perspective shifts to Glyn at Anthony’s house. She overhears Anthony telling Justine about funeral arrangements while Justine protests she should be prioritized over Glyn regarding burial decisions. Glyn enters and accuses Justine of using sex as a weapon. Justine leaves for work despite Anthony’s protests.

Glyn finds Anthony in his study, going through sketches he’s drawn of Elena over the years. When she observes he has never framed them, Glyn understands why he keeps the drawings hidden, indicating that Justine wouldn’t like it. Anthony admits Justine wanted to hurt him and make him understand how his cowardice had devastated her. He reveals he could have prevented Elena’s death by giving Justine what she wanted—a child of her own—but refused because he feared losing Elena again. Glyn accuses him of selfishness, but Anthony insists he stood firm this time, claiming this is why Elena died.