- Narrator: Marco
Marco learns that his old friend Erek is actually a robot.
Tropes:
- And I Must Scream: The Yeerk that was supposed to infest Erek instead found itself locked in a machine with its own Kandrona generator. Erek comments that it sees and knows nothing about its situation, meaning that from its point of view, its been imprisoned and it doesn't know who or why.
- Bed Trick: Touched upon again when Peter tells Marco about how much more agreeable Eva was in the year before her disappearance. Marco concludes that the Yeerk in her didn't have the time or patience to cause domestic issues.
- Been There, Shaped History: Erek and the rest of the Chee have been hiding among humans for millennia. They've occasionally been close to famous people, and given them advice that resulted in them becoming famous.
- Diabolus ex Nihilo: The Howlers were this from the point of view of the Pemalites and the Chee. Erek comments that as far as he knows, the Howlers only wanted to destroy.
- Didn't Think This Through: The Animorphs are able to reach the Pemalite crystal in bat morph, but then realize they have no way to sneak the crystal out. They're forced to assume battle morphs and tear their way out of the building.
- Dying Dream: After getting eaten, Marco sees a memory of his mother picking him up. It allows him to focus enough to demorph.
- Eaten Alive: Marco gets eaten by a crow while in spider morph. He demorphs in the crow's throat, causing it to explode from within.
- Foul Cafeteria Food: Marco calls the cafeteria food "The Goo of the Day". Jake comments that said Goo is blue, and should not be blue.
- Hostage MacGuffin: Marco is able to call off the human-Controllers with machine guns by holding up the Pemalite crystal, which could be destroyed by gunfire. The Yeerks are forced to resort to having their Hork-Bajir Controllers try to pry the crystal from the Animorphs instead.
- MacGuffin: The Pemalite crystal, which contains data that the Yeerks could use to advance their technology beyond that of the Andalites. It can also reprogram the Chee, which is Erek's motivation for wanting it.
- My God, What Have I Done?: Erek rewrites his programming, slaughters over a dozen human and Hork-Bajir Controllers each, and is so aghast at what he'd done that he changes his programming right back.
- Mysterious Animal Senses: Marco and Jake in dog morph find out that something's weird about Erek when they realize he has no smell of his own. Later on, Marco and Ax in spider morph are able to see past his hologram.
- Near-Villain Victory: The Animorphs are nearly killed by fighting twenty Hork-Bajir Controllers at once, only surviving because Marco gave the Pemalite crystal to Erek just in time.
- Perfect Pacifist People: The Pemalites were this. They had an advanced, eco-friendly society that knew nothing of violence.
- Shapeshifter Baggage: Ax reveals that the mass lost while morphing into an animal smaller than the morpher is actually temporarily sent to Z-space. The inverse is that excess matter floating in Z-space is used to add mass when morphing into a creature larger than the morpher. It's harmless— unless a ship traveling through z-space should hit a morpher's mass. The odds of that happening are a million to one, but not zero.
- Take Our Word for It: Marco was unconscious when it happened, but Erek's massacre of the Controllers was brutal enough to make Rachel cry upon remembering it.
- Too Good for This Sinful Earth: The Pemalites and their kind, pacifistic society were slaughtered to nothing by the Howlers, leaving only a few hundred Chee behind.
- You Dirty Rat!: The Animorphs get menaced by a rat while morphed into spiders and cockroaches in a vent.
