The story opens with a young boy named Danny going to a science or natural history museum. During a stroll around the museum, he immediately gets drawn to the
dinosaur exhibit. The dinosaurs in the exhibit are really models, but Danny admires them and says he thinks it would be nice to play with one. One of the dinosaurs, surprisingly a living, breathing dinosaur, responds to Danny's wish to play with a dinosaur. Both agree to play together, and Danny rides out of the museum on the dinosaur's neck. The dinosaur is well-intentioned throughout the story, learning to stop for a red light (which surprises a policeman), allowing a car to drive under him, helping people cross the street during a
traffic jam, attending a
baseball game with Danny, and taking Danny across a river. The dinosaur also becomes a celebrity, as the illustrations show hundreds of people leaving the
zoo to see him. This results in the zookeeper politely asking them to leave so that the visitors can see the zoo animals. When Danny meets up with his friends, they get to ride the dinosaur too. Then, Danny and the children all play with the dinosaur throughout the day. Finally, the children and the dinosaur play
hide and seek, as they take turns hiding. When the dinosaur hides, the children find the dinosaur several times, but then there is no place else for the dinosaur to hide in the neighborhood. In the last part of the game, Danny hatches an idea to make the game slightly harder. His idea for the dinosaur is to "pretend to not find him". When the dinosaur reveals his hiding spot, Danny and his friends all cheer for the dinosaur. At sunset, all of the children leave, and the dinosaur says goodbye to Danny. Although Danny wants to keep the dinosaur as a pet, the dinosaur mentions that the museum needs him. When Danny says goodbye to the dinosaur, he knows that he can play with the dinosaur again some other day. After watching the long tail go out of sight, Danny goes home alone. On his way home, Danny thinks about one of the things first stated in the story. He really wants to keep the dinosaur for a pet, but knows that it would be too big to live in a house. However, Danny concludes that he and the dinosaur "did have a wonderful day". ==Sequels==