While out grocery shopping, meek, middle-aged Samuel Smith and family pet Rover are run over by a speeding car. Fortunately for them, an ambulance shows up right away. Unfortunately for them, the ambulance attendant mistakenly treats Sam with dog plasma and Rover with human plasma. Both immediately recover - after which Sam starts erupting into bouts of dog-like behavior and Rover begins walking and talking like a human being, much to the consternation of the people around them, especially Sam's wife, Margaret.
Too busy reading his grocery list, poor old "Sam" and his dog "Rover" get hit by a car whilst crossing the road. I'm not sure plasma was on their list but some quick action by the medics appears to have muddled it up and so now the dog has human traits and "Sam" goes around on all fours burying bones in the garden and yapping like a maniac. "Maggie" can't make sense of this changed dynamic, especially when "Rover" refuses to eat his tinned dinner from a bowl. The role reversal aspect works quite well here and at the conclusion you don't know whether to feel more sorry for the cat hiding up the tree or the wife - well until she and her poodle meet a similar fate whilst trying to escape the madness. It's got a lively score from Clarence Wheeler and moves along quickly and quite entertainingly.