Mr. Bossi is a mean and miserly landlord in a slum tenement in the old Italian section of Brooklyn. He drives off peddlers and bill collectors by standing behind his closed office door and barking like a ferocious dog. One day a man selling fairy tales places a curse on him and pronounces that he will turn into a dog until he finds someone to love him. Mr. Bossi is suddenly transformed into a huge, homeless mongrel, reduced to sleeping in empty lots and begging for food. The only one aware of his new identity is Bruno, his meek clerk, but he is unable to help. Eventually Mr. Bossi is befriended by Tonino, a lonely youngster who gets him bones from the local butcher. A short time later, Mr. Bossi sees Giulia, one of his tenants who is an orphan, being swindled out of her inheritance by Alfonso, a neighborhood thug. The young girl hands the money to Alfonso, but Mr. Bossi leaps up, grabs the bills, and eats them. Tonino cannot forgive his new friend for this action, and the dog is once more alone. When some roughnecks attack Tonino, however, Mr. Bossi fights them off, and the child breaks the spell by professing his love for the dog. Suddenly finding himself nude (except for a dog collar), Mr. Bossi hurries back to his office. He reimburses Giulia for her lost inheritance and gives Bruno a raise so that he and Giulia can be married; Tonino is happy to remain Mr. Bossi's friend.