After their wedding, newspaper writers John and Jennifer Grogan move to Florida. In an attempt to stall Jennifer's biological clock, John gives her a puppy. While the puppy Marley grows into a 100 pound dog, he loses none of his puppy energy or rambunctiousness. Meanwhile, Marley gains no self-discipline. Marley's antics give John rich material for his newspaper column. As the Grogans mature and have children of their own, Marley continues to test everyone's patience by acting like the world's most impulsive dog.