In New York City, a man named Henry Wambach feels something dark rumbling in his gut. The feeling drives him to want to eat more and more. His hunger is insatiable. The more he eats, the more he wants to eat. Stumbling into a restaurant, his hunger becomes so intense that he tries to eat the other patrons. Eventually, though, he collapses, dead. Strangely, Henry Wambach has starved to death, despite the fact that he has eaten copious amounts of food.
In London, John Constantine arrives at his Paddington flat. He's forgotten his key in Patagonia, so he has to buzz his landlady, Mrs. McGuire to get inside. Ms. McGuire is annoyed with him for a number of reasons, foremost of which is the fact that one of John's friends invited himself into the apartment, and had her post a package for him all the way to the United States, at a cost to her of £17.50. John is suspicious of the fact that he has any guests at all, but he gives the woman £20 note, and reluctantly enters his apartment.
Relaxing into his apartment, John doesn't find anybody. He does, however, find evidence that his old acquaintance Gary Lester has been there. The place is a mess, though, and on top of that, he is down to his last cigarette. John is disgusted to find Gaz' junk needle hidden underneath a smut-rag, and he is further disgusted to see that the needle contains insects. This prompts him to investigate his apartment further. In the kitchen, the dishes have been left undone for quite some time, and the fridge is full of horrible insects, who have begun to feast on the bounty of its rotten contents. John is overwhelmed by the stench and stumbles out, only to hear some horrible sounds from his bathroom.
Inside, John finds Gary Lester, cramped in the bathtub, rambling about how his heroine withdrawal symptoms have got him hallucinating bugs crawling over his skin. He doesn't realize, however, that there really are bugs crawling all over him, and John is so disgusted that he simply slams the door. Grumpily, he goes down to the local tobacco shop and picks up some silk cuts and some bug spray before calling up his acquaintance Chaz, and having him come over.
After veritably fumigating his apartment with twelve cans of bug spray, John manages to drag Gary out of the bathroom, despite the coating of dead bugs crunching underfoot. Chaz arrives, and with his help, John hypnotizes Gary into explaining how this came about.
Gary had been in Tangiers, where he saw a young slave boy who was obviously possessed. Not only is Gary addicted to junk, though, he is also addicted to exorcism. He found the thrill of exorcising the boy so tempting that he stole him away and perform the ritual. A cloud of insects burst from the boy's skin, killing him. Desperately, Gary bound the demon Mnemoth into a bottle. But the demon tempted him from within the bottle, demanding to be let out. So, Gary's thoughts turned to John Constantine, hoping that his old friend could help. He stole a passport and sold it for a ticket to London. But John wasn't home, so Gary had the bottle mailed to the United States - to the home of John's friend Emma.
Grumpily, John assigns Chaz to look after Gary for a few days while he goes to the Sudan to find out how to exorcise the demon. John travels to a Sudanese village where a Dinka shaman is already expecting him. John explains why he is there, and then she shaman provides him with a psychedelic root to chew on in order that they can share their experience of the boy and how to exorcise the demon. The shaman had found this boy, and in order to protect his people from the hunger and famine of the demon Mnemoth, he had sealed the demon within one of the children of his tribe. However, he had not known that the boy was later found and sold to slavers. With his new knowledge, John returns to England to pick up Gary, and they go to America together.
John drags Gary (whose addictions are becoming rather grating on John's nerves) to the Midnight Club, where Haitian crime boss and Voodoo magician Papa Midnite resides. John breaks in through the back, and they are surprised to encounter one of Midnite's zombie servants attempting to capture a chicken for one of its master's rituals. The servant attacks, but a stern talking to from John sends it into submission.
John and Gary surprise Papa Midnite on the roof of his club, where John tries to convince the stern and imposing man of the fact that having a hunger demon running amok in New York will be bad for business. That said, John needs Papa Midnite's help in resealing the demon. Midnite will say only that he will consider it, as John leaves him to look after Gary.
John makes his way to his friend Emma's apartment. Gary had sent the bound demon-in-a-bottle to her address, not knowing that she had already been killed by the Invunche, some time ago. An artist is now living in her apartment, and has used her death as an inspiration for his own art. John is put out, and furthermore, regretful about Emma's demise. On the stairs outside her old apartment, John is accosted by Emma's ghost. She offers her help, and they head out into the street.
Outside, John catches sight of a man who is supposed to have been a vegetarian breaking into a butcher shop, and eating all of the raw meat there. It is clear that this is another victim of Mnemoth's influence. Unfortunately, the man dies in just a matter of minutes. John and Emma follow the trail of insects to a church. Through the great doors, John sees the demon Mnemoth in the form of a giant carrion fly. The demon is left with the choice to possess either Constantine or the priest. John dares the creature to take him, but Emma warns that he is not a strong enough magician to deal with the demon. John persists, but eventually, he is forced to run away as Mnemoth takes the priest.