At first, Fingers refuses to believe that his Granddad has gone Barking Mad! But what straight-thinking grown-up goes around licking the postman, growling like a dog and chasing hospital security guards up trees? And when Fingers and his sister Sally discover a bizarre machine in Granddad's workshop, mix-ups turn into mind-swapping madness - one look at Granddad's dog DaVinci is proof of that!