Dynamite Time presents a story within a story. Theodore Stone unexpectedly receives a letter from Julie, his nine-year-old granddaughter, the daughter of his estranged son. Julie's letter, as part of a school assignment, innocently asks, "Did you ever get into trouble when you were little?" Theodore responds with a 'to be continued' story that entices Julie into more letters. An exchange of fourteen letters tells the story of himself, as a five-year-old boy named Tad, with a Shetland pony named Dynamite. He takes her back to 1948, on a farm in rural Montana. A time when Tad wants to be a cowboy more than anything. The ongoing letters spin true adventures, both good and bad, about Dynamite, chores, mean farm animals, one-room school houses, fights, rodeos, and a variety of boyhood experiences. The exchange becomes an important part of Theodore's and Julie's lives, creating a friendship. As the stories continue, Julie's dad also becomes interested in the life of the father he never knew. This arouses hope in the empty life of Theodore. Then Julie writes, "Daddy said that you abandoned him. I have to know. Did you?" Reluctantly, he tells Julie a final story of an older Tad.