The beginning of The Gargoyle launches us into the pivotal moment of a drug addled-pornographer's life; the car accident that destroys his body and forces him to look upon the self-inflicted damage to his soul. Driving intoxicated the nameless narrator hallucinates that flaming arrows are streaking from a forest towards his car. In swerving to avoid them he hurtles off the edge of a cliff and becomes trapped inside the burning wreckage.
After awaking from a coma two months from the accident strapped to a hospital bed, he finds he has severe third degree burns that cover almost his entire body leaving him mangled, monstrous looking and without a penis. He realises he has lost the life he once had and comprehends how hollow that life really was. To comfort himself he forms an elaborate suicide plan. Then he meets Marianne Engel, an eccentric, wild haired hand-sculptor of stone Grotesques. He feels drawn to her despite her strange and mysterious behaviour and her frequent discussions in Latin with her invisible 'Three Masters'. She tells him she has to 'give away her extra hearts' to the Grotesques she carves as a penance for her sins.
As doctors help him rehabilitate his body, Marianne begins the work on his soul. She tells him that the first time they met was at Engelthal, a Monastery near Nürnberg in early 14th century Germany, when he was a mercenary burned in battle and she was the nun that tended him. After falling in love they run away together to make a new life. She is able to leave behind the strict regimes of the Constitution, and he the brutal lifestyle of his old condotta, which he has to avoid running into as the price for desertion is death.
As well as weaving their own fateful story through the contemporary narrative, the narrator also recounts Marianne’s tales of the French legend La Gargouille, and the tragic love stories that he later names as The Good Ironworker, The Woman on the Cliff, The Glassblower’s Apprentice and Sigurðr’s Gift. Marianne also reads to him Dante’s Inferno.
Once able to leave the hospital the narrator moves into Marianne's home, continuing his recovery and developing strong feelings towards her. He witnesses Marianne's manic carving sessions increase in urgency as she desperately tries to give away her extra hearts and tries in vain to stop her from wasting away as she carves. Marianne forces him to quit the morphine he has become dependent on and whilst feverish from withdrawal, he makes a voyage through his own personal Inferno-inspired Hell. He wakes up free of narcotics for the first time in years and feeling cleansed. However with Marianne’s penance complete she disappears from him for good, leaving behind a couple of significant artefacts that add authenticity to her fantastic story. The narrator is then left to contemplate his own penance. He realises he prefers the grotesque body in which he knew and loved Marianne to the body he had before she came into his life.