- Narrator: Rachel, Marco
Some kid takes a picture of the Animorphs as they demorph in an alley. At the same time, the Helmacrons return and jump up Marco's nose.
Tropes:
- And Now for Someone Completely Different: The book switched from Rachel's to Marco's point of view to keep tabs on him as he tries to solve the problem of the kid who took a picture of the Animorphs.
- Bizarre Alien Biology:
- Discussed as the Animorphs watch the Helmacrons jump into Marco's bloodstream. Half the team assumes they'll drown, but the other half correctly guesses that the Helmacrons don't breathe in the same way they do.
- A comment from Ax reveals that Andalites don't have livers.
- Delicious Distraction: Marco brings a raw steak to distract the pit bull the second time he sneaks into the apartment to steal the camera.
- Disney Death: The Helmacrons apparently succeed in killing Marco, but Marco was in roach morph at the time, so he survives long enough to demorph.
- Drama-Preserving Handicap:
- The Helmacrons knew the Animorphs would follow them inside Marco, so they tampered with their Shrink Ray. When Ax programs it, he ends up shrinking them until they're Helmacron sized to Helmacron size. As a result, they're unable to fight the Helmacrons when they catch up to them.
- Marco can't morph while the others are inside him, lest he accidentally crush them or bring the Helmacrons closer to his vitals. He's forced to find and steal the camera of the kid that took a picture of them mid-morph as a human. As soon as he does morph, the problem gets solved in minutes.
- Marco could have asked the Chee for help in stealing the camera, but his rabies-induced impatience dismisses the idea with the reasoning that it would somehow violate the Chee's no-violence programming.
- "Fantastic Voyage" Plot: The Helmacrons crawl up Marco's nose with the intent to find and stop his heart. The other Animorphs have to follow them inside. They even mention Fantastic Voyage as they fly up Marco's nose.
- Girls vs. Boys Plot: The gender war that Marco started the last time the Helmacrons showed up is still going strong in this book.
- Godzilla Threshold: Marco is told not to morph with his friends still inside him. He breaks the promise when he's nearly caught in the kid's apartment.
- I'm Melting!: The Animorphs and the Helmacrons fall into Marco's stomach and start being digested alive. The Animorphs end up okay thanks to morphing, but at least two Helmacrons don't make it out.
- My Instincts Are Showing: The Animorphs morph to shark to travel through Marco's bloodstream. The shark's mind goes haywire as it smells blood, and Rachel bites Jake's tail in a frenzy.
- Sanity Slippage: Marco slowly starts losing his composure and mental faculties after being bitten by the pit bull, who Rachel later found out was rabid.
