Third-grader Toník Burda is not very good at football so it takes a lot of persuasion for his friends Pepík and Karel to get him on the team, at least as a substitute. A fox terrier runs up to Toník on the way to the football field. As a dog owner, he suddenly gains in importance to the boys and is accepted into the game. Karel and Pepík borrow the dog - Puna as Toník calls him - but the dog runs away. The boys find the runaway in the arms of little Lidka who calls him Asa and refuses to let them have him. The boys take the dog off her and, in the tussle, the dog's nametag is lost. Toník is ashamed to admit that the dog isn't his and thus he causes a lot of worry for himself. At home he tells the fib that he is to look after the dog for a time for his teacher's friend. The lies start accumulating and the problems grow. By chance Toník is witness to a case which his father, a lawyer, has taken on for a boy convicted of theft. Toník's bad conscience eventually gets the better of him and he goes to the police. In the meantime Puna runs off to his mistress and everything is explained, both at school and at home. Toník's parents, seeing how sorry he is, buy him a puppy.
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