The death of a man at a Dionysian party on a boat has Annika thinking of Greek tragedy, especially when it turns out that a suspect is named Agamemnon.
But first, the victim. Paul Gilbride is a property developer who was celebrating the 30th anniversary of his marriage to his wife Gaynor on his boat with family and friends. His body surfaced in the River Clyde with lacerations consistent with restraints on his wrists and ankles. He was seen going below-deck around the time that the kitchen door was found to be locked for about an hour. There are traces of blood in the kitchen, a necklace with a pendant, and water all over the floor that probably came from empty water bottles. The boat’s CCTV camera was pushed away from watching the hallway.
Agamemnon, or Mem, punched Paul during the party, Gaynor’s close friend Carmela says. And there’s no record of him signing off the boat. Annika and Blair go to visit him at his property, which neighbors the Gilbrides’. He’s drunkenly shooting at wind turbines, and fires at the police as they approach. He wanted to make extra money by putting up turbines, he yells at Annika, but Paul convinced him not to. Then Paul went ahead and put up his own, while Mem was away for several months burying his mother in Greece.
But Mem is shocked when he learns that Paul is dead. He also has an out: he angrily jumped off the boat after confronting Paul and swam to shore, where CCTV cameras picked him up before Paul’s death.
Only two people signed off the boat at the stop between when Paul was last seen and when his body was found: a caterer named Veer and Paul’s godson, Gio, Carmela’s son. Gio returned to the boat after Paul’s body was discovered and drove his drunken mother and godmother home. When the police go to question him, he gets so upset when they call Paul a friend of his that he has some sort of coughing fit.
They also discover that he’s hiding a stash of cash. He says it’s savings to buy his own place—he moved home while his father was dying of cancer last year. But Paul’s business was recently broken into, and money was stolen. Gaynor tells the police Paul thought he knew who took the money, but didn’t tell the police, because it was someone he liked. She suggests Doug Macrae—they recently had an argument over business.
Paul’s assistant Louise doesn’t know of any dispute with Doug, however, or Paul’s suspicion of the thief’s identity. She reveals that Paul and Gaynor recently met with Gio at the office: something about changing the party venue.
Louise deletes some files from Paul’s laptop before handing it over.
The police discover the subterfuge and the reason for it soon, when they return to Paul’s office and find Louise having sex with Doug. Doug had argued with Paul over some shoddy work, and Louise was trying to cover up any trace of it—because she stole the money, to pay back Doug, with a little extra for herself.
Louise was below-deck at the time Paul died, and a photo showed that her black dress was torn by the end of the evening. The autopsy has revealed that Paul died of cardiac arrest, and that there was water in his lungs—not from the river—as well as black fibers in his mouth. He may have been waterboarded.
But Louise has exonerating evidence: a video of her with Doug on the boat again, at the time Paul died.
Annika continues to have her own secretive affair with Jake, Morgan’s former therapist. Both she and Morgan sneak their lovers—Morgan’s is Blair’s sister, Erin—into the house on the same night, without either noticing. Jake suggests taking their relationship public, and Annika eventually agrees, on the advice of Michael. She tells Morgan about Jake, and organizes a dinner with him.
She also knows about Erin, because Erin left her phone with Morgan and Morgan brought it to Blair at work to give back—but Morgan won’t talk about her, even when Annika tries to get her to share at the dinner with Jake. He and Morgan spend a pleasant evening together when Annika is called away for work, but it leaves him worrying that Morgan still views him as a therapist. He tells Annika they need to wait longer before dating, and she reluctantly agrees.
When Annika finally brings up Erin directly to Morgan after telling her she and Jake are taking things slow, Morgan invites Annika to join her and Erin as they fly kites on the beach.
What about the other person who disembarked after Paul’s disappearance, the caterer Veer? He was a last-minute replacement, so he was hard to track down—his roommate got sick and sent Veer instead. The roommate says Veer hasn’t left his room since the party, but when the police open the door he’s gone. He has recently been high on mushrooms a lot, and so paranoid that he moves any CCTV camera he sees—that explains the one on the boat. His search history contains variations on “Paul Gilbride death.”
But another clue leads another direction: the necklace found in the boat’s kitchen. Gaynor said Paul’s father gave it to him, and he never took it off. But Paul’s pendant was engraved; the one on the boat wasn’t. Gaynor admits that she lied about it being Paul’s; he also gave one to Gio, that he never got around to engraving.
Gio’s father died of mesothelioma, possibly from exposure to asbestos—and he helped renovate Paul’s boat, which had asbestos. Carmela and Gaynor suspected there might be a link, but the men always denied it. Gio disagreed: he secretly helped his father work on the boat, and Paul just watched. Now Gio has mesothelioma too.
When he confronted Paul, Gaynor was there. Paul’s only worry was that Gio would sue, to Gio’s disgust. Gio wanted a lawyer to find out if Paul knowingly put him and his father in danger—to get a confession. He threw the pendant at Paul in the office.
Gaynor must have picked it up. And she also borrowed a black scarf from Carmela at the party.
Annika and Michael find her on Paul’s boat, dousing it and herself in gasoline. She didn’t mean to kill Paul; she just wanted to get a confession from him, and so tortured him—but it went too far. She lights herself on fire, and Michael tackles her into the water, saving her.