The two-paragraph version: Jess arrives to stay with her half-brother Ben at his apartment in Paris, but Ben is missing. She explores the building which has an extensive wine cellar and meets the various other residents of the building.
As she investigates what happened to Ben, Jess realizes that most of the residents of the building are one family and that they make their money running an illegal sex-trafficking club (that masquerades as an exclusive club selling expensive wines). Ben was investigating and was found out by Jacques (the father). Jacques attacked Ben, but Jacques was stopped and stabbed by Mimi (the daughter who was infatuated with Ben). Jess finds Ben nearly dead and being kept in the old maids’ chambers. Ben recovers.
On Fridaythe Prologue opens with Bena journalist, working on a story in his 3rd floor apartment in Paris when someone unlocks his door and attacks him.
Ben’s half-sister Jess, who recently lost her job, shows up shortly afterwards to stay with him and realizes he is missing. She finds his wallet containing a metal card and contact information for Theo Mendelson, an editor for The Guardian.
Jess soon meets the various residents of the building. On the Penthouse floor, Sophie Meunier is an older woman whose husband is Jacques Meunier. On the 4th floor, are two young female roommates, Mimi and Camille. Mimi had been infatuated with Ben. On the 2nd floor, Nick is a single man. And on the 1st floor is a couple with an unhappy marriage, Dominique and Antoine. There’s also a lodge at the building which houses the Conciergean old woman.
On Saturday, Sophie rips up the most recent blackmail letter she has received. Sophie has been getting monetary demands threatening to expose “what you really are”, but now she feels she no longer needs to pay.
Jess finds a hidden secondary stairwell in the building that leads up to the old Maid’s Quarters at the top of the building. She also explores the building’s basement, which houses an extensive wine cellar. Nick helps let Jess out when the cellar door gets jammed, shutting her inside. Nick is old friends with Ben, and he was the one who invited Ben to stay at the building three months ago.
Jess also meets up with Theo at a café. Theo says that Ben was supposed to pitch a story to him that morning, but he has not heard from him. On the way back at the Metro, a young Eastern European woman stops Jess saying she overheard that Jess was looking for Ben. When Jess says Ben in nowhere to be found, the woman runs off before Jess can find out who she it.
Back at the apartment, Jess finds Ben’s notes about something called Le Petite Mort (meaning “little deaths”). However, when Jess goes to sleep, someone breaks in and takes the notebook containing the notes. Meanwhile, in the building’s dumbwaiter, Mimi finds a bloodied sharp object wrapped in fabric which she accidentally cuts herself with.
On SundayNick helps Jess report Ben as an official missing person to Commissioner Blanchot from the police. Nick also tells Jess about traveling around Europe with Ben and some other friends one summer in college.
Jess also gets invited into the Penthouse apartment and she finds a Russian passport belonging to Sophie. She then sees a photograph that makes her realize that the various residents of the building are a family. Sophie and Jacques are the parents of Antoine, Nick and Mimi.
We soon learn that Antoine and Nick are Sophie’s stepsons from Jacques’ first marriage while Mimi is her daughter. Jacques inherited a wine estate, the Château Blondin-Lavignewhen his first wife became ill and passed away.
That night, Mimi and Camille throw a Halloween Party. Jess attends in order to ask the various guests if they know anything about Ben, and she finds a bunch of ripped up canvases of painting of Ben in Mimi’s apartment. However, someone drugs Jess’s drink and she soon passes out.
On MondayNick thinks about the time he and Ben were in Amsterdam and he had kissed Ben (who is bisexual) which made Nick realize that he’s queer, something that Nick is deeply ashamed of.
Theo soon calls to tell Jess that he’s figured out what the metal card is from Ben’s wallet. They go to an exclusive club, and Theo explains that the card is used to get access. It’s a club masquerading as a place selling high end wine, but it is actually engaging in sex trafficking and owned by the Meunier family. Young, trafficked girls are paraded around the club and clients order “wines” so their spending seems legitimate. Jess recognizes one of the girls as the young woman she waylaid her at the Metro.
Back at the building, Sophie reminisces about how she’d been having an affair with Ben. She also thinks about how Mimi is actually her adopted child, since she was desperate to have a child of her own. (We learn that the Concierge admitted to Ben that Mimi is actually her granddaughter, and Mimi’s mother died in childbirth. Sophie then adopted Mimi as her own.)
Then, Antoine then comes in and admits to Sophie that he’s the one that has been blackmailing Sophie. He found out that Sophie was once one of the girls from the family’s club, something that Sophie has wanted to hide about her past. He demands more money and threats to tell Jacques, but Sophie refuses.
When Jess returns to the building, she’s accosted by Nick and Antoine who know about the research she’s been doing. When Antoine comes at her, Jess stabs him and runs up the stairs into the Maid Quarters to hide. She’s shocked to find Ben there – alive, but barely. Nick shows up and is confused that Ben is alive.
We then learn that on the day of Ben’s disappearance, Jacques had confronted Ben about his investigation into his family’s illegal activities and attacked him. Mimi witnessed this and stabbed Jacques before he could kill Ben. Sophie then found out and helped Mimi to cover things up. Sophie told Nick, Antoine and the Concierge that the dead body belonged to Ben (who she said Jacques had killed) so they helped to bury Jacques’ body. She also told them Jacques had left the country for the time being. Sophie then secretly took Ben (injured, but alive) to the Maid’s Quarters to hide him there.
In present day, Jess convinces Sophie to let her take Ben to get medical assistance. When Ben recovers, Theo publishes the exposé about the club while Jess convinces Sophie to provide monetary payments to the girls at the club so they can disappear (since many of them are undocumented, etc.). Jess takes a cut of the payment and starts a new life.
For more detail, see the full Section-by-Section Summary.