Travel back in time to when Marley, "the world's worst dog," was just a puppy. His owners leave him at Grandpa's house for the summer with their nephew Brodie, who's desperate to show his mother that he's responsible enough to get his own dog. He decides to enter Marley in a dog competition and with the help of grandpa and a few other friends, he teaches Marley all the tricks he'll need to know. But will it be enough to win?