- Narrator: Rachel
David returns, now sponsored by Crayak.
Tropes:
- Armor-Piercing Question: When Cassie tries to stop Rachel from going after David as he escapes, Rachel snaps back by asking her what she's planning to do about David. Cassie can't find an answer, nor can she bring herself to try harder to stop Rachel.
- Badass in Distress: Rachel and Cassie are trapped by David and Crayak, held in small, but durable boxes peppered with insecticide, meaning they can't morph out if they wanted to.
- Broken Tears: Rachel and David cry together as David begs Rachel to kill him, while Rachel tries to hold on to Nice Rachel by taking him back to the island, which she knows is Cruel Mercy.
- Catapult Nightmare: The book opens with one where the Animorphs are touring the White House just as the Yeerks make the invasion public. Rachel saves the president, but disobeys Jake's orders in the process, causing him to chew her out, and her to respond as Mean Rachel and trying to fight him. She loses, and wakes up screaming.
- Deal with the Devil: Crayak gives his offer to Rachel once more, only this time using previews of her new powers and confusing tortures to get her to agree.
- Death Seeker: With his plans foiled and no hope of becoming a human again before his rat lifespan runs out, David begs Rachel to kill him. It's up to the reader to decide if she does.
- Dream Within a Dream: Rachel wakes up from a second nightmare after her first where she gets the idea that Jake is trying to keep her from taking over the team, and then nearly crashes into a radio tower resembling Crayak's eye.
- Elephant in the Living Room: The other Animorphs are no longer hiding how disturbed they are by Rachel actively enjoying any chance to fight the Yeerks, despite how outgunned they are.
- Gladiator Games: As a preview for what he can give her, Crayak gives Rachel the ability to morph into any creature she needs without having to acquire or know it even exists, and pits her against Visser One. She wins, but refuses to kill him when she has him at her mercy.
- Good Shapeshifting, Evil Shapeshifting: Rachel is gifted with upgrades to her powers that break all the established rules of morphing. As a result, she easily proves herself in a Shapeshifter Showdown against Esplin, outfighting the Visser for the first time in the entire series... only to realize that the new powers are designed to corrupt her into another one of Crayak's pawns, encouraging her Blood Knight tendencies and getting her Drunk on the Dark Side.
- Hallucinations: While at school, Rachel starts seeing Crayak's eye on her and hearing rats within the walls. While the sensible answer is that she's seeing things, a definite possibility is that Crayak is Gaslighting her.
- Mind Screw: Rachel's insanity and Crayak's ability to warp reality around her on a whim make for a story where it's very hard to follow what's real and what isn't.
- One-Winged Angel: Crayak grants Rachel a "Super Rachel" form, featured as her cover morph. She get taller and more muscular, with Wolverine Claws and the Super-Strength to match. On top of that, she can morph to anything she need in a few seconds.
- Rat King: Subverted. David claims that he can now command swarms of rats, but that turns out to be a lie. Rachel is able to get him to admit that the rat swarm was actually Crayak's doing.
- Riddle for the Ages: Did Rachel kill David in the end? The book ends with her looking at her own and David's reflection and thinking about how an outsider would see a girl in a leotard crying as she looks at a white rat.
- Sadistic Choice:
- Rachel is forced by David to morph to rat, lest he close Cassie's box all the way to make her suffocate.
- The majority of the book is Crayak psychologically tormenting Rachel to get her to agree to become his minion. She manages to refuse.
- Sanity Slippage: Rachel's narration has almost completely fallen to Mean Rachel's half of her personality. She's feeling like the rest of the group's problem is a lack of faith in her abilities, and has become paranoid enough to believe that Jake feels like his leadership is being threatened by her.
- Screw This, I'm Outta Here:
- Crayak and the Drode leave Rachel to her fate when she refuses to kill Visser One against all odds.
- The two punks that David recruited leave when it becomes apparent that David is nothing more than a talking rat who can't pay them anything and Rachel coerces them into releasing her so she can savage them.
- Stranger in a Familiar Land: This is the last book to feature any of the Animorphs in school. Rachel feels a disconnect from all of her classmates, even Cassie, and she can't bring herself to care about class or homework anymore. Rachel describes the scenes in the school itself are narrated as though she's watching everything through a Plexiglass window.
- Sparing Them the Dirty Work: Rachel believes at this point that this is her contribution to the Animorphs. She has to be the one who "takes out the trash", because none of the others have the guts to do it.
- Swarm of Rats: Rachel and Cassie are captured by one, leading to the reveal that David is an antagonistic force in this book.
- Through the Eyes of Madness: Rachel's final narrated book shows her giving into her nature as the Blood Knight who keeps all the other Animorphs' hands as clean as possible. To make matters worse is Crayak manipulating reality around her to the point where she doesn't know what's real.
- Your Approval Fills Me with Shame: While Rachel hates how her friends look at her these days, complimenting her about her bloodthirsty aggression makes her feel worse.
- You Have Outlived Your Usefulness: Much to the Drode's horror, he realizes that if Rachel does become Crayak's minion, he'll be out of job.
