BLOODY MOON is Jess Franco's entry into the 'stalk-and-slasher' genre. Miguel is a disfigured young man who was sent to a mental home for murdering a girl with a pair of scissors after a party. Five years later he is released. His sister Manuela is in a relationship with a language teacher Alvaro. Even though she loves Alvaro there is something in her relationship with her brother that is holding back her unconditional love for Alvaro.

After the death of the siblings' rich wheelchair-bound aunt (who hated Manuela) gruesome murders begin happening at the school where Alvaro teaches.