The film follows the story of Trelkovsky (played by Roman Polanski), a shy and reclusive man who moves into a Parisian apartment after the previous tenant, Simone Choule, has committed suicide. Trelkovsky’s new home is a small, dilapidated apartment in a building with a suspiciously odd and unwelcoming atmosphere.

As Trelkovsky settles into his new apartment, he begins to experience strange and unsettling occurrences. The other tenants in the building are peculiar and seem to have a collective sense of hostility towards him. He also starts to notice disturbing changes in his own behavior and mental state.

Trelkovsky becomes increasingly paranoid as he uncovers disturbing secrets about the previous tenant and the apartment itself. He starts to believe that the apartment is somehow influencing his mind and that he is being driven towards the same fate as Simone Choule. The line between reality and delusion blurs as Trelkovsky’s mental state deteriorates, leading to a series of psychological and supernatural events.