Tanner feels lonely. Sundays are his family's usual day to plan an outing, but it appears everyone is too busy on this day to have fun. Just when he is about to give up, Tanner's parents surprise him with plans to drive to Castle Rock Park for a picnic. After Tanner, his parents, and new baby brother meet up with his Nana, Papa, and other family members, he takes in the sights of the park that is surrounded by tall mountains and a sheer face cliff called Elephant Buttress. But when Tanner asks to take a walk to a nearby stream, he has no idea that very soon, he will meet a friendly rock climber who will teach him all sorts of important lessons about nature, the environment, teamwork and, above all, how to trust others and believe in himself. Sunday at Castle Rock Park shares the fun tale of a boy's adventure at a local park after he meets a rock climber who teaches him valuable lessons about life, nature, and himself.