Fleeing from their violent father, siblings Lucía and Adrián take refuge in a remote mansion. With the help of a hidden micro-camera on a cat, Lucía uncovers a terrifying secret: their neighbors are part of a criminal network that kidnaps teenage girls to make snuff films, and they intend to get rid of the siblings. As Lucía fights to protect her brother, she must face a dark family curse that follows them into their newfound sanctuary.

Laura and her father Wilson arrive at a cottage off the beaten path in order to repair it since its owner will soon put the house on sale. They will spend the night there in order to start the repairs the following morning. Everything seems to go on smoothly until Laura hears a sound that comes from outside and gets louder and louder in the upper floor of the house. Wilson goes up to see what is going on while she remains downstairs on her own waiting for her father to come down. The plot is based on a true story that occurred in the 1940s in a small village in Uruguay. La casa muda focuses on the last seventy eight minutes, second by second, as Laura tries to leave the house unharmed and discovers the dark secret it hides.