The Prophecy (Animorphs #34)

There is a chance for the free Hork-Bajir on Earth to start their own rebellion against the Yeerks. They have the numbers, but they don't have the weapons. They've learned from the last surviving Arn -- the race that created the Hork-Bajir -- that Aldrea, daughter of Prince Seerow, knew the location of a stolen Yeerk vessel.Unfortunately, the only way to recover the ship is to ask Aldrea herself -- and she's dead. The Arn have Aldrea's persona stored, but to bring her back, they need a host body