The kids let Marmaduke outside to greet their father Mr. Winslow as he gets home from work. Once inside there is a knock at the door. It's the police and a member of the lost pet society who claims that Marmaduke is actually the lost dog of Mrs. Van Upton named Hobart. They two men haul off Marmaduke upsetting the entire Winslow family. The kids follow Marmaduke in an effort to get him back.
The Winslow's are on a trip to the supermarket and Marmaduke is trying to help drive. When they finally get parked Mr. Winslow accidentally leaves his keys in the car as Jake and Grugsy Glugg come out of a bank that they have just robbed. Little do they know that Marmaduke is in the back seat and plans to foil their robbery.
Heathcliff and Iggy are competing against Muggsy and Spike in the annual Pet 'N Pal Cross-Country Sled Race and the winner gets a gold trophy and all the pizza they can eat at Luigi's Pizza Parlor. Will Heathcliff and Iggy be able to overcome all of the obstacles that Spike and Mugsy put in their way and win the race?