Jim and Barney are in trouble. The boat's engine won't start and they've got to get to Jim's grandson's birthday party, so they get a big, strong horse named Puzzle to give them a tow.
Barney and Puzzle become firm friends, with Puzzle trusting Barney to help him along the way.
Although Jim finds Puzzle a bit of a handful, all goes well until the horse is frightened by some pigs and gallops away.
It's up to Barney to find Puzzle and make sure they get to the birthday celebrations -