Rachel is falling apart, literally. Her newest morph has the ability to regenerate its limbs but when Rachel remorphs there's a lot more Rachel than when she started out. One more Rachel, to be exact. Rachel is an okay parson to have around but two could be considered overkill. Especially two Rachel with completely opposite personalities: one is pathetically weak, one is super strong and super nasty. Now the Animorphs have to figure out the way to put Rachel back together again.