The four canine friends from Hound's Glenn - Max, Theena, Edgar, and NicNac - are back! They're enjoying Summer Science Camp, taught by their favorite teacher, Ms. Chienne, when Edgar's big brother, Harold, comes up with a surprising plan. The most cautious and responsible driver in town, Harold suddenly decides to invent a new kind of racing car. He wants to take it to All Critters City for the big race and auto show. Unfortunately, because of a bridge collapse on the main highway (a passel of pigs shouldn't do the sway on a suspension bridge), it look like Harold's dream is finished. But Max, Theena, Edgar, and NicNac are as inventive as ever, and they'll find a way. At the summer school outing to the water slides in River Otter City, they discover an old steam-powered riverboat that looks like it can get Harold and his car to AC City in time. Along the way, we meet the boiler-stoking bears from Minersville, and Casanova Cugat, the most inept pirate ever; Theena makes a new friend, a beautiful puma singer; the eight-hundred-pun gorilla finds a new job; and our four furry friends invent a way to save the riverboat and the day. In the spirit of "Alice in Wonderland" and the "Uncle Remus" stories, the cast of feathered, scaled, and furry characters in Harold and the Hot Rod have a great deal of fun, and some of them create a bit of mischief and get their just deserts. Themes of friendship, inclusion, and fair play underlie the humor and adventure.