Elin is a police detective from the United Kingdom who is currently on an extended leave of absence. She suffers from severe anxiety and trauma following a brutal incident involving a previous suspect named Mark Hayler. She travels to the luxury hotel Le Sommet to celebrate her estranged brother's engagement, though she finds the isolated setting unsettling. As a snowstorm traps the guests, her investigative instincts take over when people begin to disappear.

Isaac is a former computer sciences lecturer and Elin's older brother. He recently became engaged to Laure Strehl and invites his estranged sister to Switzerland to celebrate. He left home years ago and maintained very little contact with his family, even during their mother's final illness. He presents a confident exterior but harbors deep emotional scars from his family's past.

Laure is the assistant manager at Le Sommet and Isaac Warner's fiancée. She grew up as a close childhood friend of Elin, though the two lost touch as adults. Laure appears poised and confident in her professional role, working long hours to ensure the hotel runs perfectly. Her sudden, unexplained disappearance shortly after Elin's arrival sets the central mystery in motion.

Lucas is a prominent real estate developer and the owner of Le Sommet. He transformed the property from an abandoned, historical sanatorium into a minimalist luxury resort, fulfilling the legacy of his great-grandfather who originally designed the building. He is highly protective of his business, often downplaying the controversies and protests surrounding the building's dark medical history.

Cecile is the manager of Le Sommet and Lucas Caron's sister. She takes meticulous care of the hotel's daily functions and guest relations. She acts as a buffer between her brother and the staff, ensuring the property runs smoothly despite the impending severe weather. She is highly protective of Lucas and the hotel's success.

Will is an architect and Elin's boyfriend. He appreciates the minimalist design of Le Sommet and hopes the mountain getaway will help Elin relax and heal from her work-related trauma. He is practical and grounded, viewing the vacation as a chance to repair their strained relationship.

Margot is a spa receptionist at Le Sommet. She interacts frequently with the guests and observes the dynamics among the hotel staff. She shares a room with a younger employee named Sara and provides Elin with background details about Laure's recent behavior and the tensions among the management.

Daniel is the architect originally hired to design Le Sommet. He is a childhood friend of Lucas Caron. His sudden, unexplained disappearance during the construction phase delayed the hotel's opening by a full year and remains a lingering mystery among the local community.

Adele is a cleaning lady at Le Sommet. She is a young mother who is eager to finish her shift and return to the valley to see her son, Gabriel, before severe weather traps her on the mountain. She notices strange items left in the rooms she cleans, drawing her into danger.

Sam is Elin and Isaac's deceased younger brother. He died as a young child after falling onto rocks in a tide pool while hunting for crabs. The tragic circumstances of his death cast a long shadow over the Warner family, creating a permanent rift between his older siblings.

Inspecteur Berndt is a local Swiss police officer. Because severe weather and an avalanche prevent his team from reaching the isolated hotel, he reluctantly relies on Elin to secure evidence, interview witnesses, and monitor the situation on the ground until help can arrive.