By way of a simple mosquito bite, Ozzy and Drix are transferred into the body of a 13-year-old boy, Hector. Unfortunately, a nasty germ named Scarlet Fever is also transferred, and our heroes have to capture him before he wreaks havoc on the City of Hector.

Ozzy accidentally produces a neural spasm that causes Hector to kick the school bully. When the bully threatens to beat up Hector after school, Ozzy has to figure out a way to help Hector defend himself.

Ozzy becomes jealous of a super agent (Penicillin G) who has been injected into Hector to track down a powerful germ known as Strepfinger.

When Ozzy discovers there are lice eggs in Hector's hair, he and Drix venture onto the scalp to knock the eggs off, only to end up running into the monstrous Mother Louse!

Drix's new pet dog, Dander, is mistaken for a Allergen that is threatening the city.

Drix tries to learn how to act ""street"" and ends up helping an acne germ create a huge zit on Hector's face.

Ozzy, Drix and Maria commandeer a submersible police craft into the intestines to stop a gas build-up that threatens Hector's social situation.

Ozzy must keep Nick O'Teen from getting to the brain where he will cause Hector to smoke.

When Sal Monella, a poisonous gangster germ, kidnaps the Mayor with plans to poison Hector, Ozzy and Drix must come to his rescue.

Ozzy thinks he's going to have a baby, but it turns out he's been infected with an intracellular bacteria by returning villain Strepfinger. Ozzy and Drix must find a way to destroy the parasite growing within Ozzy before it spreads its infection to all of Hector.

The Mayoral election is coming up, and Spryman's opponent, a nerdy brain cell named Sylvian Fisher, is using a secret growth formula to cause destructive growth spurts and make the Mayor look bad. Ozzy and Drix must stop this fiendish plan, which becomes more difficult when Sylvian takes the growth formula himself and becomes a raging, muscular monster.

Hector binges on candy, creating a sugar rush that speeds up all the cells and causes the bacteria population to swell. When his parents cut him off sugar, his drop in blood sugar slows all the cells to a crawl. But the bacteria need sugar, so they form an army to raid Hector's sugar reserves. Now Ozzy and Drix, with the help of the Mole, must take on the bacterial army.

Hector's terrible recurring nightmare is keeping everyone in the City of Hector awake. Ozzy and Drix go to the ""Subconscious Network,"" where dreams are produced, and enter Hector's nightmare to help him face his fear.