When a mosquito bite transfers Ozzy and Drix into the body of a boy, Hector Cruz, another germ comes with them. It is up to Ozzy and Drix to capture this germ, Scarlet Fever, before it has disastrous consequences.
Ozzy crashes his car into a nerve causing Hector's leg to fly out. Normally that wouldn't be much of a problem, but this time Hector accidentally tripped the local school bully, getting him into a fight after school.
As Hector finds a stray dog outside, an allergen is wrecking Hector's insides. The size changing allergen alternates between a huge monster and a meek guy. At the same time Drix finds a pet dog cell of his own.
Ozzy, Drix, and Maria commandeer a submersible police craft into the intestines to stop a gas build-up that threatens Hector's social situation and infects him with gastroenteritis. Maria is desperate to stop the build up because one gas attack Hector had killed her father and she is determined to avenge him. However, the Rota Virus captures her and ties her up with rope and struggles to get free.
Hector has been hanging with the cool kids at school and tried smoking. This has brought in the addictive Nick O'Teen and his associates who want to enslave all cells in Hector.
Hector eats a tainted corndog from the rusty dog stand and gets salmonella. Now Ozzy and Drix have to save the day and the mayor from the toxic germ Sal Monella.
The Mayoral election is coming up and Spryman's opponent, a brain cell named Sylvian Fisher, is using a secret growth formula in order to cause destructive unnatural growth spurts and hurt the Mayor's image. Ozzy and Drix must stop this plan, which becomes more difficult when Sylvian takes the growth formula himself and becomes a raging and muscular monster.
Hector has been eating lots of sweets lately, causing his sugar levels to go out of whack. The energy dip afterwards has left all cells sluggish. At the same time, a large amount of bacteria has grown from all the sugar and have been raiding the sugar supplies.
