The following version of the novel was used to create this study guide: Ware, Ruth. One by One. Gallery/Scout Press, September 8, 2020. Kindle.

In the murder mystery One by One by Ruth Ware, when members of the tech company Snoop begin dying during a ski vacation to discuss a buyout, they worry there is a murderer among them. Shut off from society in a chalet damaged by an avalanche with no cell phone or Internet service, the survivors decide to split up to find help. Unknowingly, they isolate the most vulnerable of the group with the killer.

Danny and Erin, the staff at Chalet Perce-Neige, sense the tension among Snoop employees following a surprise presentation by Eva van den Berg, one of the co-founders, the first night of the retreat. Eva wants the company to take a buyout offer, but Topher St. Clair-Bridges, the other co-founder, wants to retain control of the company. Adding to the mystery is Liz Owens, a plain, working-class woman who does not seem to fit in with the other employees. Erin learns both Eva and Topher are trying to woo Liz because she owns two percent of the company. Based on the split of employees wanting to keep the company and wanting to sell it, Liz will cast the deciding vote.

The first morning that the group goes out to ski, Eva does not return to the chalet with the others. Because of heavy snow, cell phone and Internet service is spotty so Erin decides to take the funicular to town to see when Eva last used her lift pass. As she is leaving, an avalanche mows down the mountain hitting and damaging the chalet. Erin suffers what Danny believes is a broken ankle, but Erin argues it is just a bad sprain. Even though no one else has cell phone service, Inigo gets one bar of service on his phone and is able to contact the police for help. Making matters worse, the electricity goes out later that day.

The next day, Topher and Elliot talk to Danny and Erin in private because Elliot has used a new update on the app to locate Eva’s phone. Topher is excited and believes they should get a search party together, but both Erin and Danny know that if Eva is where her phone indicates she is, she has skied off the side of the mountain and is dead. Danny and Erin hold a meeting later that day to formally announce their suspicions that Eva is dead. Ani goes upstairs to get Elliot, who has not joined the others, and discovers he is dead. Because Elliot’s computer has been smashed to bits, Erin and Danny believe that he was murdered because of something he knew. With this in mind, they acknowledge the possibility that Eva was murdered as well.

Wondering if Ani, who believed she saw Eva skiing down the black run, had told anyone else what she saw, Danny and Erin questioned Ani. Ani said she remembered telling Carl, and she believed Inigo, another member of the party, had heard. Ani is angry when Carl suggests she has just incriminated Inigo. Ani goes to Inigo’s room to question him, but discovers he is gone. He has left behind a note that says he made a terrible mistake and is going to make it right. No one knows what he is talking about.

The next morning, Ani is discovered dead. She has been smothered in her sleep even though she and Tiger shared a room for safety and locked their door. Danny discovers someone has stolen his master key. It is assumed that the person who stole the key is the one who killed Ani. Because the police have still not come, the group decides to split up and go for help. Danny, Carl, and Miranda snowshoe to a nearby chalet in hopes they have a satellite phone or radio they can use to get help. Topher, Tiger, and Rik ski down to the village to alert help. Neither Erin nor Liz, who hurt her knee falling down the stairs, can ski so they stay at the chalet.

While Erin and Liz are together, Erin finds the staff key in the cushions of the couch where Liz was sitting. She infers that Liz is the killer. Liz, meanwhile, realizes that Erin knows she is the killer and tries to decide what to do. She knows she cannot kill Erin because there would be no way to hide that she is the killer.

Liz tells Erin about an incident when she was working for Snoop when Eva dressed Liz up and took her to a party. They visited a man’s private residence after the party. The man sexually assaulted Liz and Liz pushed him away. She says her push accidentally sent him over the side of the balcony on which he was standing, a fall he did not survive. Later, Liz makes tea for Erin. She spikes the tea with sleeping pills, hoping to kill Erin and make it look like a suicide. Erin only pretends to drink the tea. She sneaks out of the chalet and skis down a treacherous run to the valley to save herself. Liz tries to follow her but is unable to stop in time to avoid slamming into a rock wall. She dies as a result of the impact.