A group of tourists arrive to see the botanical gardens on a small island off the Italian coast. The only inhabitants of the island are the famous botanist Baron von Weser and his two faithful servants; all of the other residents fled after a series of mysterious deaths. When the car driven by the tourists' guide hits one of the baron's servants, von Weser explains that the death was due to a rare and incurable disease, not the accident. That night, the guide and Cora Robinson, one of the guests, are found murdered with all the blood drained from their bodies.

Francisca, es huérfana de madre, su padre la abandonó, comparte piso con Raquel y accede a pasarse por la esposa de Cesar, el novio de Raquél para que éste consiga un trabajo. Pero por el piso aparecen su padre, su madre que creía muerta y su novio Rufino.