Today is the big unveiling of the Ankylosaurus dinosaur skeleton at the Museum, but it's missing a leg! George and the Man with the Yellow Hat thought they delivered all 4 bones. Where did the 4th bone go? Fortunately, Mr. Quint took pictures on their way to the Museum. Maybe the photos can lead them to the bone...if they can only figure out which order to put them in. George and Allie's imaginations run wild as they brainstorm what could be in the large unmarked box on George's doorstep. Based on its weight, sound, smell, and bristly hair, they're certain it's a baby goat! But what's really inside surprises them more than anything they could have ever imagined.