Sleepwalkers features Charles Brady and his mother, Mary. Charles and his mother are Sleepwalkers or shapeshifters who lives by absorbing the lifeforce of virgin women. Normally, they appear as humans by they can also change into bipedal werecats when they want to. They also possess certain powers like telekinesis and making illusions. However, they are vulnerable to cats and their claws. The creatures are not fooled by illusions and they can easily injure sleepwalkers with their claws.

Charles and Mary start living in a small Indiana town where Charles continues his studies in the local high school there. In the school, Charles flirts with one of the students, Tanya Robertson, intending to make a victim out of her later on.

During their first date, Charles tries to absorb Tanya’s lifeforce but she struggles and escapes. As she flees from Charles, Tanya runs into Deputy Sheriff Andy Simpson. Charles kills the sheriff and resumes going after Tanya. However, it seems that the sheriff has brought along with him his cat which at that moment, attacks Charles and seriously injures him. Charles retreats and seeks the care of his mother. Mary on the other hand, cloaks themselves to avoid the authorities who are searching for them.

To help her dying son, Mary kills Tanya’s family and takes Tanya hostage. She brings her to their house so Charles can take her lifeforce. Charles attempts to absorb Tanya’s lifeforce again but she manages to kill him. Mary however, is killed by the group cats led by the sheriff’s pet. The film concludes with Mary burning to death and Tanya holding onto the sheriff’s cat.