The one-paragraph version: the Thursday Murder Club gets involved in a new case as Elizabeth’s ex-husband, Douglas (a MI5 agent), shows up asking for help since he stole 20M in diamonds and is in hiding. When he winds up dead, they investigate. It’s eventually revealed that he stole them with help from Sue, his contact at MI5 who he was romantically involved with. However, Douglas planned to betray her. When she found out, she killed him. She then kept working with Elizabeth to try to uncover the location of the diamonds.
(This book picks up very soon after the previous novel ends with the same main characters — Elizabeth, Joyce, Ritchie and Ibrahim — at the Coopers Chase retirement community.)
In Part I, Elizabeth is revealed to be a former MI5 (British intelligence) agent, and she receives a letter from a “Marcus Carmichael”, a fictional person whose death she once faked as part of her work for MI5, asking to meet. Elizabeth shows up at the proposed and finds her ex-husband Douglas, there. He’s still active in MI5, and he’s accompanied by his handler, Penny, who is young and inexperienced.
Meanwhile, while Ibrahim is out in town, he gets randomly attacked with his phone stolen, and he’s hospitalized. Officers Donna and Chris determine that the perpetrator is Ryan Baird, a local teenager who works with a drug dealer they’ve been trying to build a case against, Connie Johnson. However, there’s insufficient evidence to charge him.
Douglas tells Elizabeth that he needs her help since he stole 20M in diamonds from Martin Lomax, a man who works as a middle-man for various crime organizations (like drug lords, mafiosos, warlords, etcetera). MI5 doesn’t know he stole them. He’s hiding out in Coopers Chase until he can escape to Antwerp, sell the diamonds and disappear. Douglas wants Elizabeth’s help in keeping a look-out for possible threats.
Elizabeth agrees to help in exchange for information on Ryan Baird, and Poppy soon gives her the file on him. Soon after, an intruder tries to shoot Douglas, but Poppy kills the intruder. Sue and Lance from MI5 arrive to clean up the scene. Poppy is shaken up from killing someone, and Elizabeth and Joyce try to comfort her. When Douglas and Poppy are taken to be questioned by Sue and Lance, Joyce finds a note in her pocket from Poppy asking Joyce to call her mother, Siobhan, along with a phone number. Joyce obliges, tells Siobhan what happened and invites her to tea.
Meanwhile, Elizabeth has a plan regarding Ryan and asks her friend Bogdan to acquire come cocaine. Bogdan does it and hands it off to Ron. Ron then goes to Ryan’s house, pretending to be a plumber sent by the housing association. He plants the cocaine and Ibrahim’s credit card in Ryan’s toilet and then “anonymously” calls Donna and Chris. Ryan Baird is arrested.
By now, the dead intruder has been identified as Andrew Hastings, one of Martin Lomax’s lackeys. Also, Douglas and Poppy have been relocated to a nearby town. Douglas asks Elizabeth to come see him there, and she agrees. However, when Elizabeth and Joyce arrive, they find Douglas and Poppy are both dead, having both been shot in the face (making them both barely recognizable).
In Part II, Elizabeth and Joyce are questioned about the discovery of the bodies. Sue gives Elizabeth a locket inscribed with her name that they found on Douglas’s body. Siobhan identifies Poppy’s body.
Afterwards, Elizabeth goes to see Martin Lomax who is anxious to get the diamonds back since they’re not his. He was holding them (as the middle-man) for a deal between some American mafia guys and some Colombians. If he can’t locate them, they’re threatening to kill him by the end of the week. Lomax admits to sending Andrew to scare (but not kill) Douglas, but he insists he wasn’t responsible for the shootings. Meanwhile, Lance at MI5 flags a fight that Frank Andrade Jr. (American mafia guy who owns the diamonds) is on headed to Fairhaven, likely for the purpose of killing Martin Lomax.
Later, Elizabeth recalls that Douglas had pointed out a hole in a tree, which he’d commented would be a good place for a dead-letter drop (a public place spies use to leave stuff to be picked up). Sure enough, when Elizabeth checks that spot, she finds a letter addressed to her from Douglas. It says that the diamonds were hidden in Locker 531 at the Fairhaven train station. If they’re still there by the time she reads this letter, it means he’s dead. If they’re gone, it likely means he somehow faked his death and escaped with the diamonds.
Meanwhile, Chris and Donna have continued to investigate Connie Johnson. Chris has also continued seeing Donna’s mother Patrice (who he met towards the end of Book #1) romantically. Connie drops by Chris house and threatens to hurt Patrice is Chris continues looking into her activities. Additionally, Ryan failed to show up for his court date and is nowhere to be found.
When Elizabeth and Joyce get to the train station, they find an empty chip bag in Locker 531. Elizabeth uses an infra-red light on the bag, and it reveals a hidden message. It says that this is an extra layer of security, that the diamonds are elsewhere and that Elizabeth should be able to figure out where. Elizabeth also asks Donna to procure the CCTV footage to see if anyone else has visited the locker. They eventually learn that Siobhan (Poppy’s mother) had visited the locker the day before the shooting.
In Part III, Elizabeth figures out where the diamonds are — she notes that there was a mirror in the locket that Douglas had on him and that he’d previously referenced a dead-letter drop in East Berlin which she knew was really in West Berlin. She figures out that those were hints that Locker 531 was meant to be inversed — and that the diamonds are in Locker 135. Elizabeth and Joyce recover the diamonds and take them home and hide them away.
Elizabeth theorizes that if Siobhan was the one visiting the locker, then Poppy must’ve found out about Douglas stealing the diamonds and gotten Siobhan involved in her scheme. Poppy could’ve overheard Douglas telling Elizabeth the truth (that he stole them) and then killed him and faked her own death (since Siobhan, her accomplice, was the one who identified her body).
From there, Elizabeth formulates a plan to get some answers. She plans a meeting with Martin Lomax at the pier saying she’ll give him the diamonds there. Then, when Frank Andrade lands in Fairhaven, she intercepts him and instructs him to attend the meeting as well if he wants his diamonds back. (Her plan is to force Poppy to come out into the open when Poppy realizes the diamonds have resurfaced and that this big meeting is taking place.)
As for Connie, they (Ron and Bogdan) invite Connie to attend the meeting telling her that it’s an opportunity for her expand her drug trade. So, they tell Connie to bring Ryan Baird with her to drive her to meeting (claiming that he’s someone they trust). Connie knows where Ryan is, so she agrees. (The idea is that by involving Connie and Ryan, it’ll implicate them in an illicit deal, and they’ll be conveniently present to be arrested.)
When the big meeting arrives, Frank, Martin and Connie meet up (with Bogdan and Lance in the room, too, and everyone else is safely outside). Frank gets upset when he realizes his diamonds aren’t there, and he shoots Martin. Connie then shoots Frank before he can shoot her. She then tries to leave, but is promptly arrested by Chris and Donna (who were waiting outside). Ryan is also arrested. Poppy does not show up.
Afterwards, Elizabeth and Joyce are in a car with Sue, and Elizabeth now confronts Sue about being the real killer. After Poppy failed to appear, Elizabeth figured out that things were less complicated than they seemed and there were no faked deaths. Poppy and Douglas are both dead. Instead, Elizabeth realizes that Sue must’ve been the one to put the note in Joyce’s pocket about Siobhan, not Poppy. Sue purposely wanted them to think “Siobhan” was Poppy’s mother (to set them on a false trail of investigating Poppy), when in reality “Siobhan” was really Sue’s accomplice.
Sue admits that she and Douglas planned to steal the diamonds together since they were romantically involved. Poppy later overheard Douglas telling Elizabeth about the diamonds and hinting at the dead-letter drop. Poppy then found the letter to Elizabeth (in the hole in the tree) and obediently told Sue about it. Sue read the letter and realized that Douglas planned to betray her, so she told Martin where Douglas was. When the guy Martin sent failed to kill Douglas, Sue did the job herself and shot Douglas (and killed Poppy in the process).
In present day, Sue tells Elizabeth that she has three armed dudes working for her and they’ve located the diamonds at Joyce’s house. Sue has the driver take them to Joyce’s — but as soon as they arrive, Sue is shot by Bogdan. (It’s soon revealed that Bogdan incapacitated the three armed dudes and told them to tell Sue that they’d found the diamonds.)
In the final chapters, Chris tells Patrice that he loves her, Bogdan decides to ask out Donna and Joyce adopts a dog named Rusty. The book closes by revealing that Elizabeth ended up fencing the diamonds in Antwerp and then donating the money to an organization called Living with Dementia (because her husband Stephen has dementia).
For more detail, see the full Section-by-Section Summary.