Danny goes to the museum where his wish comes true - a friendly dinosaur comes to life and spends the day playing with him. As the dinosaur says, after one hundred million years, it's good to play outside! The two have a monstrously good time eating ice cream, going to a ball game, and playing hide-and-seek with Danny's friends. When the day comes to an end, the dinosaur must return to the museum, even though Danny wants to keep him as a pet. After all, the museum needs him, and, Danny realizes, the dinosaur probably wouldn't fit in his house!