Bozo's circus sets up near the "Great Tar Pits." The noise from the cannon wakes up a dinosaur in the tar pit who causes chaos until Bozo lures him back into the tar. In attempt to get the dinosaur back, the circus owner sets off explosions, which cause an earthquake. Bozo and his friend Sparky fall through a fissure into an underground lake which leads to the catacombs of the tar pit, which contain giant animals and a race of people called the Tar Men. Bozo makes their King laugh and as a reward is given the giant animals. The Tar Men give him two potions, one which will shrink the animals, the other that will make them large again. Bozo's spiteful old circus boss destroys the enlarging potion, but Bozo's circus is still a success with the miniature animals.; After trying to make the door to his circus wagon fit, Bozo ends up with a small square that is just the right size for a birdhouse.; Bozo buys a crying boy a balloon, then finds that he was tricked.; When Bozo misses the circus train, he goes to buy an automobile. He can't afford anything but a used tire.