The Journey (Animorphs #42)

The Animorphs' latest adventure takes them where no man has ever gone before… into Marco's left nostril. Who else could be responsible for this mess but a crew of miniature egomaniacs? The Helmacrons have returned to demand the morphing cube because they need more power to escape Earth's atmosphere. In the middle of their threats, Rachel tries to destroy their ship, and some of the little warriors bail… right into Marco's body. Rachel and the others must follow them in order to help Marco. But to make matters worse, Marco's on a mission to recover a photograph that could give away the secret of the Animorphs. He has to do some serious chasing of his own, which could require morphing. And if Marco has to morph, who knows what will happen to his friends on the inside….