Ax wishes to return to the Andalite home world, and to do so, he needs a ship. He intends to build a communicator to broadcast a Yeerk distress signal and lure in a Yeerk ship which he can then hijack. He goes to the mall to buy the equipment to build a communicator. He finds the food court and runs wild sampling food left over on tables. He is chased by security guards and, frightened, demorphs in the middle of the mall in front of many people. He, Jake, and Marco run out of the mall and into a nearby grocery store where they are chased by Controllers. They morph into lobsters and hide in a tank. They later escape.

Ax builds his device, but needs a zero-space transponder. Mr. Hedrick Chapman regularly communicates with Visser Three from his basement, so the Animorphs morph into ants and retrieve the Z-space transponder that he uses. As they are returning from Chapman's house, they are almost killed when attacked by ants from another colony. They are able to demorph in time.

Ax completes his device, and broadcasts the signal, but the Yeerks have changed their distress frequencies, and, sensing a trap, they set one of their own. The Animorphs are captured (in animal morph) and taken aboard the Yeerk mother ship, where Visser One is visiting. Visser One confronts them and her host body is Marco's mother, who is alive after all. The Animorphs are put in a cell, and they are freed by one of Visser One's Hork-Bajir; Visser One and Visser Three are rivals, and Visser One wanted to disgrace Visser Three. The Animorphs reach an escape pod and return to Earth.

Marco's father returns to work. Marco asks Jake, the only one who had previously met Marco's mom, not to tell any of the others about Visser One.