One by One by Ruth Ware is a contemporary psychological thriller published in 2020. Set at a ski chalet in the French Alps near the town St. Antoine le Lac, the story is told from the alternating perspectives of two women: Liz, a shy, lonely woman who does not fit in with the rich socialites with whom she travels, and Erin, a private woman with a scarred face and a tragic past. The book discusses topics like survivor’s guilt, class disparity, and post-traumatic stress disorder.

One by One is an homage to the novel And Then There Were None (1939) by Agatha Christie. In Christie’s novel, eight people arrive on an isolated island, met by a butler and housekeeper. It is the best-selling mystery novel of all time, with more than 100 million copies sold.

Other works by this author include The Turn of The Key, One Perfect Couple, and The Death of Mrs. Westaway.

This study guide references the 2021 Simon & Shuster Inc. paperback edition.

Plot Summary

The novel opens with the “About Us” page from the smartphone application Snoop, followed by a BBC news article about a fatal avalanche in the French Alps that is being investigated as murder. The novel then skips to five days before the news article, with the narration alternating between Liz’s and Erin’s first-person points of view.

Liz is a shy woman who is accompanying the eight members of the Snoop staff to a ski chalet in the French Alps. Her companions are Topher and Eva, cofounders of the app; Elliot, who writes code for the app; Rik, the company’s chief financial officer; Miranda, who heads media relations; Tiger, who manages wellness and design; Carl, the company lawyer; and Ani and Inigo, both personal assistants. Erin is a host at the Chalet Perce-Neige who, with the chef Danny, ensures that guests have a perfect experience.

The Snoop team arrives, and it is obvious that Liz does not fully belong with the group. After an uncomfortable moment when Erin realizes Liz was not on the original itinerary, drinks and snacks are served. Eva holds a surprise presentation, during which she discusses the potential buyout that Snoop has been offered. This upsets Topher, who does not want to sell the company. Dinner is tense, and afterward Erin overhears Miranda and Rik talking about Liz. Rik tells Miranda that Liz invested money into the company before the application launched, and as a result, she possesses 2% of the company’s voting shares, worth approximately £12 million in the event of a buyout.

The next morning, Erin awakes after a nightmare about digging in the snow and gets the chalet ready for the day. She learns from the town baker that the avalanche warning is “considerable.” As the guests wake up, they plan to ski in the morning and conduct business meetings in the afternoon when the weather worsens. Erin teaches the guests the routes and observes that Liz is not a confident skier, feeling pity for the woman.

The morning passes and it begins to snow, but Topher convinces the group go to the top of the mountain and take one more trail before lunch. The others agree and split up into groups to take the bubble lifts to the trails—one an easy blue trail, and the second a very difficult black trail. Topher is mad because the black trail has been closed. Liz has a panic attack and takes the bubble lift back down.

Back at the chalet, Erin and Danny are frustrated with the guests’ tardiness. The group returns late, and they realize that Eva is not among them. Ani claims she saw Eva taking the black trail from the bubble lift, recognizable for her bright red ski jacket. Right after Erin leaves to get the police, an avalanche crashes down the mountain. Danny helps Erin, who has broken her ankle, back inside. Inigo manages to get cell signal and calls international police while everyone’s thoughts turn to Eva.

The electricity goes out and tensions rise. Elliot and Topher attempt to track Eva using a GPS update to the Snoop application, but Erin breaks the news that if the information is accurate, Eva is dead. Following the news, Topher realizes he is the majority shareholder of the company. He gets very drunk, insists that he knows Erin from somewhere, and sleeps with Ani.

The next morning, Liz wakes up cold and reflects on her childhood bedroom, where she experienced abuse at the hands of her alcoholic father. She goes downstairs to chat with Elliot, who eventually claims he has urgent business to discuss with Topher. Erin and Danny call a meeting to discuss survival plans, and Ani goes upstairs to get Elliot. She finds him dead in his room with his computer destroyed. Erin, who dropped out of medical school, determines that he was killed and deduces that he may have been murdered to hide something about Eva’s death.

Different members of the group make accusations about who could be involved in Eva’s and Elliot’s murders, and Rik verbalizes a suspicion that Inigo never called the police. Inigo runs from the room and later leaves the chalet to go to the police for ambiguous reasons. The group decides to sleep in pairs to protect themselves, but Liz refuses to share a bedroom with anyone. Late that night, Ani arrives at Liz’s room to implore Liz to share a room with her and Tiger. She says she has a feeling, and Liz pressures her to share everything she knows about Eva’s death. Ani goes back to her room, and Liz has a hard time sleeping.

They awaken the next morning to Tiger screaming, having woken up to find Ani dead in bed beside her. Erin identifies it as suffocation, which Tiger did not hear because she takes sleeping pills. Danny realizes that his staff key, which grants him to access every guest room, is missing. When Erin and Danny gather everyone downstairs to talk about what happened, Topher recognizes Erin as Lady Dorothea de Plessis FitzClarence, the youngest daughter of the Marquess of Cardale. Danny leaves the room, and Erin follows to explain while Topher reveals to the others that she was the sole survivor of an avalanche that killed her brother, Alex, and lover, Will, three years prior.

Danny and Erin reconcile. After discussion and debate, the members of Snoop decide to split up. The better skiers will go to St. Antoine le Lac, while the weaker skiers will trek to Chalet Haut Montagne, the nearest other ski resort. Erin will stay behind due to her injury. While preparing, Liz falls down the stairs and injures her knee, causing Danny to go in her place. While waiting for the others, Liz and Erin play cards and share information about their pasts. Liz talks about the excitement of joining Snoop at the beginning, while Erin opens up about the avalanche that took Alex’s and Will’s lives. After dinner, Liz goes upstairs to collect bedding, and Erin finds the missing staff key where Liz was sitting. In the night, Erin goes upstairs to Elliot’s room and uses his corpse’s thumb to access his phone, sending a text to Danny. While looking through his notifications, she investigates Snoop’s GPS tracking capabilities. She realizes that the last person to see Eva alive was Liz. She now suspects that Liz is the murderer. Liz comes upstairs and goes to her room, checking her suitcase, which contains a scarlet ski jacket.

Danny texts back, but Liz gets to the phone before Erin does, and the two of them realize there is no point in lying anymore. They go downstairs, and Liz tells Erin her story. When she joined Snoop, she invested her money, and Topher convinced her to take the voting shares instead of a loan because she would be easily bullied into voting with him. The Snoop staff went to an investor event, taking Liz with them. When Liz, Eva, and an investor went to a second location for drinks, the investor assaulted Liz, who killed him in self-defense.

Liz attempts to poison Erin with sleeping pills in tea, but Erin recognizes the taste and pretends to fall asleep. She then crawls out of a window with her skis, planning to take a secret ski route to St. Antoine le Lac. Liz follows, and the two women race through the dark, treacherous path. At a hairpin turn, Erin manages to brake in time, but Liz crashes into a cliff face at full speed. She is killed on impact.

Paramedics find Erin, and she is taken to the hospital. After several days, she is taken to a bed and breakfast and reunites with the others. Topher is sent a file from Eva’s husband that contains proof of Liz’s story, as well as blackmail directed at other investors. Several weeks later, Snoop declares bankruptcy, and Erin receives an apology email from Topher. The chalet is closed, meaning that Erin and Danny have lost their jobs. Danny decides to stay at St. Antoine le Lac to work for the bed and breakfast. Erin decides to go home to England and mourn Alex and Will with her family. The two say a tearful goodbye, and Danny tells Erin to sign up for the new music application Choon.