Painter Horace visits his friend, a former criminalist, and is intrigued by two strange women who live in the house opposite. The old sisters have lived together their entire lives, quarreling, doing things to each other on purpose, but they cannot be without each other. And then one day both sisters are found dead in their locked apartment. They poisoned themselves with gas. Officially, the case is closed as a suicide. But Horace doesn't think so... Even though his criminalist friend discourages him, he continues his investigation. Were the women murdered? And is Janza involved, or their friend Pesný, who was supposed to live in their apartment?
