Louis and his sister find themselves deep inside the stomach of a Saber-toothed Yumper when a leisurely bike ride through the woods turns into a monstrous chase into prehistoric lands. After Louis is swallowed by a Gulper, Sarah sets off to rescue him, but each creature that consumes him is set upon by a larger one, and the chase is on. Finally, she must crawl into the stomach of the Saber-toothed Yumper and, flashlight in hand, wind her way through the insides of all the other beasts to retrieve her brother. Although the situation resolves itself when the creature feels a real "frog in its throat," the siblings are not free to return home until one of them finds a more vocal way to scare away the still-hungry Guzzler, Grabular, Undersnatch, and Gulper. Fardell cleverly morphs verbs into the names of the monsters chasing Louis and a two-wheeled bicycle into a machine capable of floating, rock climbing, and flight. The antics are over-the-top, and the creatures are more funny than scary, making this picture book a natural for storytime fun