The Yeerks are tracking morphing energy and it's a race against time to try to keep them from stealing the morphing cube and becoming truly unstoppable. Cassie must keep running at all costs. But the cube is dangerous in itself, and the Animorphs didn't count on the gruesome implications of allowing the cube to be taken out in the open. When the cube comes into contact with innocent animals the effects are truly horrifying - now Cassie's got more than the Yeerks to worry about...