Miss Popper's first grade class is taking a field trip to the firehouse. Carlos wants to play a trick on his classmates, so he hides in the back of the fire truck. But the joke is on Carlos when the alarm rings, and the firefighters are called to an emergency. Lucky for Carlos, it's not a fire; it's a cat stuck in a tree. The firefighters are too heavy to climb the tree, so it's up to Carlos to save the day!