The Devil's Elixirs is predominantly a first-person narrative related by the Capuchin monk Medardus. He is ignorant of his family history and what he knows about his childhood is based upon fragments of memory and a few events his mother has explained to him.

Medardus cannot resist the devil's elixir, which has been entrusted to him and which awakens in him sensual desires. After being sent from his cloister to Rome, he finds a Count, disguised as a monk as a means of seeing his lover, and pushes him (whether intentionally or not is ambiguous) from a "Teufelssitz" ("devil's perch"). Unbeknownst to all involved, the Count is Medardus's half-brother and the Count's lover is his half-sister. The Count becomes his lunatic doppelgänger and crosses his path multiple times after Medardus abandons his ecclesiastical position, drifting throughout the world.