Frank's desire for obscure sexual pleasure lead him in search of an infamous puzzle box that was known to unlock a world of pleasure and delight not known by any man.
Upon finding the box he returned to the house of his lover, the wife of his brother Rory. While in the house he locks himself in an upstairs bedroom and solves the box, opening a realm inhabited by demons (cynabites) whose form of pleasure more closely resembles torture and pain than the sexual delights he was looking for. Frank is drawn into this realm and is not heard of for sometime.
Frank's brother Rory and his wife Julia are moving their things in to the house one day and Rory severely cuts his hand on a nail and the blood spills on the floor of the bedroom that Frank solved the box in. The blood disappears into the floorboards and a hideous creature arises from the floor to feast on the blood and the rats that inhabited this room. Julia discovers this creature one day and learns that it is Frank, who was allowed to escape the realm by feasting on the blood that spilled on the floor and needs more to become whole again.
Julia begins to seduce men while Rory is at work and lures them back to the house so that Frank can feast on their bodily fluids and have Julia dispose of the bodies. During this time, Rory's friend Christy, becomes suspicious of Julia feeling that she is having an affair and follows her one day...discovering that she is bringing men home. She learns of the hideous creature upstairs and flees the house after stealing the puzzle box from Frank. The police do not believe her story and she is placed in the hospital overnight. While at the hospital she solves the box and the demons appear and demand blood for opening the box. Christy explains to them about Frank returning from the realm and they do not believe her. She bargains with them that if she will bring them to Frank, they will spare her and take him back with them instead.
Christy returns to the house to find Rory and Julia sitting at the kitchen table looking upset. She is told that Rory killed Frank and that the problem is solved and that they are in love again. Christy does not believe them and rushes upstairs and sees the skinned body of Rory on the floor and realizes Frank is wearing Rory's skin.
A fight and chase ensues, eventually resulting in Julia tricking Frank into admitting that it is indeed him wearing Rory's skin, which triggers the cynabites to appear and tear Frank apart and take him back with them. Christy runs down stairs and sees a beheaded Julia with a cynabite, who gives Christy back the puzzle box. Christy runs out of the house and throws the puzzle box in the bushes.
A homeless person finds it.