Martha loves her daily walks. She enjoys sniffing and scratching with her pals down by the hydrant. But today something is different. A house down the street has been sold, the for sale sign replaced by a new sign--BEWARE OF DOG! Always curious, Martha investigates and discovers that there's a new dog in town, a blustering tough-dog named Bob. He's big and mean, and even Martha reluctantly concedes that he may be a bad dog.