An ambitious young executive (Dane DeHaan) travels to the Swiss Alps to retrieve his boss from a "wellness spa," only to find that his boss has vanished. He is then trapped in the facility, and begins to realize that its staff have a far more wicked plan than to simply improve the health of their patients. While held at the spa, he encounters a young girl named Hannah (Mia Goth), a longtime spa patient who is oblivious about what horrible things the spa director has prepared for her.

As the young man’s sanity is tested, he discovers that he has been diagnosed with the same outlandish illness that keeps all the patients at the spa hoping for a cure.