A young boy who detests taking piano lessons, Bart Collins (Tommy Rettig) has developed a deep suspicion of his strict instructor, Dr. Terwilliker (Hans Conried). Raised by his single mother, Heloise (Mary Healy), Bart looks up to the local plumber August Zabladowski (Peter Lind Hayes). When Bart ends up in a Seussian dreamworld, he must join with Zabladowski to rescue his mom from Dr. T's clutches and stop his plan to force 500 boys to play a massive piano in perpetuity.