Two strange sisters live in a crumbling mansion, where they keep a pet ape, which belonged to their late father, locked in a cage. While one of the sisters seems to be keeping her head on straight, as it were, the other appears to be sinking further and further into barbarism and insanity.

Ellen, una astrónoma de éxito, cuida de su hermana Cissy, enferma mental, que tiene una variedad de primates en la casa que heredaron de su padre antropólogo. Cuando Ellen comienza un romance, los celos de Cissy resultan mortales.