- Narrator: Cassie
The Animorphs decide to boost their numbers.
Tropes:
- Achilles in His Tent: Jake spends the first half of the book sullenly refusing to engage with anyone in the valley. Losing his parents to the Yeerks along with his brother messed him up to the point where he has a hard time getting into his role as the leader, despite the situation being more critical than ever.
- Brutish Bulls: Kelly chooses a bull as her battle morph.
- Deus ex Machina: Jake is being strangled by Visser One's morph, and it looks like he'll be killed... then a Hork-Bajir Controller cuts the tentacle, and blends in with the rest before Visser Three can retaliate. Cassie can only assume that Yeerk was a member of the Yeerk Peace Movement.
- Disabled Means Helpless: Played with. The Auxiliaries are offended if anyone thinks this of them, but the majority of them can't even run away when out of morph. When in morph, they're no less dangerous than any other Animorph.
- Disability-Negating Superpower: James and two other Auxiliaries are healed of their disabilities after they demorph for the first time. The rest have congenital disabilities that can't be healed by morphing.
- Downer Ending: While Cassie and the Auxiliaries are able to save the other Animorphs, the Yeerk in Tom gets away with the morphing cube because Cassie stopped Jake from being able to catch him.
- Everybody Knew Already: Collette claims she was rendered paraplegic in a skiing accident. In reality, she was born without the use of her legs, which she only admits when morphing doesn't heal her. The other Auxiliaries knew the truth, because they could see her chart.
- Gut Feeling: Cassie claims that this is why she let the Yeerk in Tom get away with the morphing cube. She doesn't know why it was the right thing to do, but it's still the reason why she stopped Jake from pouncing on him, and didn't bother chasing after him herself.
- Inspirationally Disadvantaged: The Auxiliaries have far less trouble controlling their morph instincts than any other morpher seen so far. Cassie concludes that their disabilities give them better mental discipline, especially for the ones incapable of normal movement.
- King of Beasts: Much like David before him, James acquires a lion as his battle morph. Jake is the only one of the Animorphs who doesn't take it as a bad omen, and he's right to do so.
- The Millstone: Naomi keeps trying to escape the valley and contact the authorities, who are all Yeerk-controlled by now. Rachel's attempts to argue with her about this are brushed off, and Naomi simply starts making plans to escape again.
- Never Smile at a Crocodile: Collette chooses a crocodile as her battle morph.
- Nothing Is the Same Anymore: Cassie is forced to reckon with just how much she and the other Animorphs have changed since the war began via her interactions with her father Walter. When he hears that the group has recruited a group of disabled kids to become an auxiliary team, he scolds her for being so amoral. Cassie ultimately realizes that he's right, but knows that she did what was necessary, and has to admit that she and her friends have lost their childhood innocence forever.
- Recruit Teenagers with Attitude: The Animorphs acknowledge that only fellow teenagers would be willing to fight impossible odds and take orders from other teenagers, which is why they dismiss adults as potential recruits.
- Tears of Joy: James cries as he walks on his legs for the first time in ten years.
- Teeth-Clenched Teamwork: The Animorphs have fallen into this, with each of their Fatal Flaws rubbing each other the wrong way. The parents make things worse, as half of them don't understand what's at stake, or have a misguided faith that the authorities can handle the war better than the kids can.
- Wham Episode: Thanks to Cassie, the Animorphs lose the morphing cube to the Yeerks.
- What the Hell, Hero?: Walter tries calling Cassie out for recruiting disabled children to help fight a war. Cassie recognizes that she was once in his shoes, and gets angry because he still doesn't understand how crucially the Animorphs need the help.
