The DDT, the professor Bacterio's dangerous invention has just been stolen by the dictator of Tirania. The Súper wants to recover it but he knows that it should not call Mortadelo and Filemón, so it sends the case to a boaster detective called Freddy Mazas so that recover the invention, but Freddy is bribed by the dictator Tirano. The mission seems that it will fail although Mortadelo and Filemón investigate the case for their own means.