When Tim and Mary befriend a small dog at the playground, they are delighted as he surprises them with a very friendly smile. The children become the victims of two mean bullies, but a mysterious voice saves them. Where did it come from?

Later, when flying their kites, the siblings are once again interrupted by the bullies. Tim lets go of his kite and it begins to fly away, until the small dog catches it and then astonishes the youngsters by speaking. The children promise to keep his secret so that their new canine companion is not taken away.

After another incident with the bullies, the children find the little dog wounded and take him to the vet. The vet examines him, including his unique vocal cords, and bandages him up. Recovering and taken home by the children, the dog relates his extraordinary story and tells the children that his name is Tadcaster.

Will Tadcaster be able to stop the bullies once and for all?