- Narrator: Jake
A mission to shut down a hospital that turns its patients into Controllers ends with Jake being infested by a Yeerk.
Tropes:
- And I Must Scream: The first narrated view of what being a Controller is like. Jake can still think and feel, but the Yeerk is in complete control of his body, leaving him unable to even scream in thought-speak. To make matters worse, the Yeerk can review his memories, fantasies, and dreams, leaving no room for privacy in his head.
- Ant War: Temrash tries escaping as an ant, only to encounter the same problem that the Animorphs narrowly survived in the previous book.
- Creepy Cockroach: The cockroach morph isn't anywhere near as bad as the ant, but it's still considered gross by the kids. Ax wonders why humans are afraid of roaches.
- Defiant to the End: Subverted. Jake notes that Yeerks with nothing to lose will surrender against impossible odds, whereas a human in the same position will fight to the end. This saves his life, as Temrash is unable to force the Animorphs to kill Jake.
- Despair Event Horizon:
- The fate of any long-time Yeerk host. Temrash gleefully reveals that Tom used to be just as defiant as Jake is now, but ended up broken by months of mental torture.
- Also the fate of any Yeerk that dies of Kandrona starvation. While in the fugue state, Temrash loses his ability to keep his memories from Jake, stops talking altogether, and dies with no hope that he'll be rescued.
- Early-Bird Cameo: As Temrash 114 dies in his head, Jake sees a glimpse of Crayak.
- Early-Installment Weirdness:
- Ax says it takes several minutes for a Yeerk to subjugate a new host, hence why Jake is still himself for a short while. This never happens again in the series, where Yeerks take immediate control of any new host body.
- Temrash 114 claims to have previously been Temrash 252 before a promotion, indicating that Yeerks with lower numbers are higher ranking in their empire. This becomes inconsistent when considering that Visser Three's real name is Esplin 9466, and Visser One's is Edriss 562, which would make them both lower ranked than Temrash if this rule still applied.
- Eye Scream: The second time Temrash tries using Jake's falcon morph, Tobias catches him with his talons as soon as he shrinks and threatens to put out the falcon's eyes and see how far he manages to fly after that. Temrash is forced to give.
- He Knows Too Much: Tom followed a girl he had a crush on into a Sharing meeting, saw Visser Three's Andalite host, and was subsequently dragged to the Yeerk pool.
- Helpless Observer Protagonist: Jake spends the last third this book mentally arguing with a Yeerk named Temrash. At first, he tries to fight back and warn the others, but he can't. Fortunately, Ax Spots the Thread, so his friends tie him up in the woods and constantly monitor him until Temrash dies.
- Hostile Terraforming: Temrash confirms Ax's comment in book #4 about Yeerks destroying the natural ecosystem of the planets they conquer to make them more like their homeworld.
- Hugh Mann: Ax has to impersonate Jake for his family, and doesn't tone down any of his own quirks when doing so. Jake's parents and Tom's new Yeerk are weirded out, but not enough to suspect Andalites.
- Humanity Ensues: Visser Three reveals his human morph to his underlings and the Animorphs for the first time. Ax wonders why they're surprised, since they know Visser Three can morph and humans have DNA that can be acquired by morphers.
- Implausible Deniability: Temrash screams "Get your hand off me, Andalite filth!" at Ax, then tries going back to pretending to be Jake and passing his outburst off as having a bad day. None of the Animorphs are fooled.
- Inopportune Impersonation Failure: For a moment, it looks as if Temrash might have the opportunity to escape and hand the Animorphs over to Visser Three... and then Jake finds himself face to face with Ax. Yeerks aren't too fond of Andalites, and Temrash can't stop himself from letting his disgust show on his face - immediately revealing the truth to Ax. The rest of the Animorphs are dubious, but then Ax touches "Jake," prompting Temrash to let out an enraged scream of "Andalite filth." From then on, the Yeerk's attempts to continue the performance are all shot down by the various team-members.
- My Life Flashed Before My Eyes: As Temrash starves, Jake sees its own memories, from the first time it infested a Gedd, to the Hork-Bajir, and then Tom.
- No Body Left Behind: Temrash decays to nothing after starving to death.
- Ominous Owl: From the Temrash's point of view, a great horned owl begins attacking him in the darkness when he tries using Jake's peregrine falcon morph. The owl turns out to be Cassie in morph.
- Out-of-Character Moment: Temrash 114 lets its mask slip several times.
- As Tom, he gives Jake a look of utter contempt when the latter refuses to join the Sharing.
- As Jake, he gives a look of disgust at Ax, giving himself away. Then he refuses to let himself be quarantined for three days, which the real Jake would allow.
- Properly Paranoid:
- Visser Three assumes that any animal nearby could be an Andalite bandit in morph. Killing any animal seen in a Sharing meeting would be seen as excessive if he was never right about it, but 10% of the time, he is.
- The other Animorphs decide they need to quarantine Jake in case Ax is right and he has been made into a Controller, which he has.
- Sapping the Shapeshifter: The Animorphs themselves make use of this against Temrash. Because he'll die of starvation if he can't get to a Yeerk Pool within the next three days, he continuously attempts to escape his captors via Jake's morphing abilities... only to be countered each time by a series of traps set up for him by the other Animorphs, each one wearing him down through progressively more dangerous stakes until he's forced to surrender. In one case, he attempts to flee the area as an ant, only to blunder directly into an ant nest and almost gets ripped apart before he can demorph - whereupon he surrenders to the observing Animorphs. This works so well that Temrash ultimately gives up after nearly three days of failures and resigns himself to a slow death by Kandrona starvation.
- Sauna of Death: The Yeerks in the hospital jacuzzi get boiled alive when Jake increases the temperature of their pool. Temrash 114 escapes this fate when Jake is knocked into the pool by a bullet's ricochet.
- Sleeps with Both Eyes Open: Yeerks can sleep when their hosts sleep, but they don't actually need to. Jake has his recurring nightmare for a while, then wakes to find that Temrash has been up and alert the entire time.
- Smug Snake: Temrash 114 starts out confident that he can fool the Animorphs, then confident that he'll escape them, then confident that his Yeerk allies will come to rescue him, all while gloating about Yeerk superiority and mentally torturing Jake. It never happens, and Temrash dies of Kandrona starvation.
- Vomit Discretion Shot: Rachel excuses herself to barf when she sees Cassie morph into a fly.
- You Have Failed Me: One Controller is dumb enough to assume the cockroaches they saw are just normal cockroaches. Visser Three exasperatedly orders said Controller to be shot dead on the spot.
