- Narrator: Tobias
Sub-Visser 51 returns with a proposition for Tobias.
Tropes:
- Artificial Limbs Are Stronger: Taylor's prosthetic arm is strong enough to punch away Tobias in Taxxon morph and punch a hole through a metal pipe.
- Badass in Distress: Tobias is captured by Sub-Visser 51 early in the book. She lets him go with the proposition to meet up again with her later.
- Broken Tears: Cassie is forced to fight her way through the pumping station's workers in order to shut off the gas and save her friends and all the hosts in the Yeerk pool. When the other Animorphs find her, she's in tears and no comfort will reach her.
- "Could Have Avoided This!" Plot: Cassie contacts Mr. Tidwell and finds that the time that the Yeerk Peace Movement feeds is the same time that Sub-Visser 51 planned to blow up the Yeerk pool, something the other Animorphs didn't know until after the plan is foiled.
- Crapola Tech: Ax builds a computer with internet access with the latest late 90s technology. It takes him hours to set it up, the website loads at dial-up internet speeds, and when Sub-Visser 51 finally gets and responds to their messages, it crashes. Ax is visibly unimpressed afterwards.
- Diabolus ex Machina: Tobias has just helped save a missing child and is feeling good about himself... then a golden eagle attacks him, injuring him and causing him to fall into the hands of a wildlife rescue team, who are then attacked by Yeerks looking for what they know to be an Andalite bandit.
- Did You Actually Believe...?: Sub-Visser 51 asks this of Tobias once her real plan becomes apparent and he rejects her offer to join her. He didn't, but tells her he did to get her to keep talking.
- Dramatic Shattering: Sub-Visser 51 smashes her coffee mug after Taylor surfaces to warn Tobias about trusting the Yeerk.
- Evil Makes You Ugly: Tobias notices that his Taylor morph gets more male attention than the real deal despite both of them looking identical. He knows it's because Sub-Visser 51's barely-restrained unhingedness scares off any boy that she approaches, even if they don't know why.Tobias's narration: We were mirror images, literal carbon copies. But I was alive. Taylor wasn’t. Not really. I had a sense of humor. Taylor had a coldness that enclosed her like a shield. The kid could see this. Anybody could.
- Fake Defector: Sub-Visser 51 claims to now be a member of the Yeerk Peace Movement, which is becoming more radical thanks to Visser Three's subjugation. It's a lie, and her real plot is to take out the actual Yeerk Peace Movement and the Andalite bandits in one fell swoop.
- False Flag Operation: The Yeerks pretend to have an Enemy Civil War over the captured Tobias to make it look like he can make an uneasy ally out of Sub-Visser 51.
- Gender Bender: Tobias acquires Taylor in an attempt to slow down his kidnapping. It doesn't work, but it does give him the perfect morph for meeting Sub-Visser 51 in a public area later.
- Heel–Face Turn: Taylor has turned against Sub-Visser 51 since her last appearance, briefly regaining control of herself to warn Tobias against trusting the Yeerk infesting her.
- Heroic RRoD: Taxxons will dig and dig, becoming more desperate for food, until they collapse and die from exhaustion. This nearly happens to Tobias and Ax when they lose themselves while digging.
- Horror Hunger: Tobias and Ax acquire and morph into a Taxxon for the purpose of digging their way into the Yeerk pool. It only takes seconds before the Taxxon's hunger overwhelms them and tries to get them to eat their friends, though Ax discovers a semi-hibernation state that makes the Taxxon hold still.
- I'm Melting!: When Ax morphs to Taxxon, it's described as his Andalite body melting into a puddle before a Taxxon inflates itself from the remains.
- Mark of Shame: Ax explains that using a tail blade to shave the fur of an unruly warrior is a standard punishment for Andalites.
- Nature vs. Nurture: Tobias muses on this as he listens to the instincts of Taylor's body. He finds no cruel Alpha Bitch, but a kind, gentle girl who's afraid of the real Taylor. He concludes that Taylor must have been nice before high school and the house fire that disfigured her made her into what she is today.
- No Good Deed Goes Unpunished: Tobias leads a rescue team to find a missing child, speaking to the child's father as he does so. When news of a talking hawk breaks out, the Yeerks immediately begin gunning for him.
- Outside-Context Problem: Sub-Visser 51 is stumped by Tobias's ability to acquire her host while "in morph". Tobias misleads her by hinting that the Andalites are continuing to improve the morphing technology.
- The Paralyzer: Taylor's prosthetic arm hides a paralytic spray that can affect several large animals at once, allowing Sub-Visser 51 to get the better of Jake, Marco, Rachel, and Ax so she can talk to Tobias alone.
- Psychic-Assisted Suicide: Sub-Visser 51 forces Taylor's body to punch through a gas pipe and ignite it, revealing she doesn't care if Taylor dies in the explosion since her plastic skull means she will survive.
- Regret Eating Me: Tobias caught a squirrel that bit him on the talon. Rachel questions him about the wound later, leading to this exchange:Tobias: <Breakfast sometimes bites back.>
Marco: You’re telling me. I was looking in the toaster to see if my Pop-Tart was done and wham, the thing shot out and hit me in the eye. - Removed Achilles' Heel: Yeerks will die when their hosts do. But because Taylor was rebuilt with plastic, right down to her skull, all Sub-Visser 51 needs to do is disengage from her brain and wait out the gas explosion so other Yeerks can recover her later.
- Rhetorical Question Blunder: The exchange between Marco and Ax after they hear Sub-Visser 51's plan.Marco: Is she insane?
Ax: Yes. I believe we established that during our last encounter. - Rouge Angles of Satin: Ax mistypes EarthIsOurs.com as EarthIsaurus.com, and comments on how his fourteen fingers are too much for a human ten finger keyboard.
- Screw This, I'm Outta Here: Cassie angrily rejects the idea of blowing up the Yeerk pool with all the innocent hosts inside. When the others decide to go along with Sub-Visser 51's plan, she storms away and doesn't come back until the end.
- Trauma Button: Tobias met Sub-Visser 51 ten books ago, yet he can still hear her screaming at him at the slightest reminder of her. Even his Taxxon morph freezes in fear of her rather than keep eating.
- Tunnel King: Taxxons dig by eating through dirt and rock, then ventilating the material through a gill like structure that holds the tunnel together. The Taxxon morph can dig much faster and more efficiently than the mole morph used in The Underground.
- Uncertain Doom: Taylor and Sub-Visser 51 are last seen being blasted away by pressurized flammable gas, which the Animorphs barely survive. Neither one appears again after this book.
- Unwitting Pawn: Tobias knows that Sub-Visser 51's plan to destroy the Yeerk pool is a trap, but he goes along with it anyway. It's only after the plot is foiled that he learns that the time when the Yeerk pool would have been destroyed was the time when the most members of the Yeerk Peace Movement were feeding, meaning Visser Three was planning on killing two birds with one stone.
- We Can Rule Together: Sub-Visser 51's ulterior motive was to some how convince Tobias to let her infest him and take down the Yeerks in charge of Earth's invasion together. He rejects her offer.
