The narrator, Egaeus, is a studious young man who grows up in a large gloomy mansion with his cousin Berenice. He suffers from a type of obsessive disorder, a monomania that makes him fixate on objects. She, originally beautiful, suffers from some unspecified degenerative illness, with periods of catalepsy a particular symptom, which he refers to as a trance. Nevertheless, they are due to be married.