The Doctor Will See You Now: Dr. Sax

Wiki:

Doctor Sax (Doctor Sax: Faust Part Three) is a novel by Jack Kerouac published in 1959. Kerouac wrote it in 1952 while living with William S. Burroughs in Mexico City.

The novel begins with Jackie Duluoz, based on Kerouac himself, relating a dream in which he finds himself in Lowell, Massachusetts, his childhood hometown. Prompted by this dream, he recollects the story of his childhood of warm browns and sepia tones, along with his shrouded childhood fantasies, which have become inextricable from the memories.

The fantasies pertain to a castle in Lowell atop a muted green hill that Jackie calls Snake Hill. Underneath the misty grey castle, the Great World Snake sleeps. Various vampires, monsters, gnomes, werewolves, and dark magicians from all over the world gather to the mansion with the intention of awakening the Snake so that it will devour the entire world (although a small minority of them, derisively called "Dovists," believe that the Snake is merely "a husk of doves," and when it awakens it will burst open, releasing thousands of lace white doves).

The eponymous Doctor Sax, also part of Jackie's fantasy world, is a dark, but ultimately friendly, figure with a shroud black cape, a inky black slouch hat, a haunting laugh, and a "disease of the night" called Visagus Nightsoil that causes his skin to turn mossy green at night. Sax, who also came to Lowell because of the Great World Snake, lives in the forest near the town, where he conducts various alchemical experiments, attempting to concoct a potion to destroy the Snake when it awakens.

When the Snake is finally awakened, Doctor Sax uses his potion on the Snake, but the potion fails to do any damage. Sax, defeated, discards his shawdowy black costume and watches the events unfold as an ordinary man. As the Snake prepares to destroy the world, all seems lost until an enormous night colored bird, an ancient counterpart of the Snake, suddenly appears. Seizing the Snake in its beak, the bird flies upward into the heartbreakingly blue sky until it vanishes from view, leading the amazed Sax to muse, "I'll be damned, the universe disposes of its own evil!"