The Helmacrons are back, and this time they're determined to get hold of the morphing cube. Despite their size, they have devised a sure-fire way of getting the Animorph's attention-they're inside Marco, and they're heading for his heart. (Well, there's a few things that being a millimetre and a half tall is good for.) The Animorphs must take them on, but that means shrinking, and a battle...and the battlegrounds is Marco's body. Thing is, Marco's got his own mission-a kid captured him morphing on camera. He's got to find it and destroy the evidence, but as long as the Animorph s are inside him, he can't morph. Can he succeed without his most important weapon?