The adventure begins when a spy breaks into Professor Bacterio's lab and steals some of his inventions from the T.I.A. headquarters (''Técnicos de Investigación Aeroterráquea''). Mortadelo and Filemón who work for the T.I.A. are put on the case, but Fredy, another agent, decides to beat them to it. One of the inventions is a weather control machine which the spy decides to sell to the President of Tirania, a small Eastern European dictatorship. There are numerous clashes between the spy, Fredy, and Mortadelo and Filemón (who Fredy seems to want to kill). Our heroes end up in prison after accidentally beating up the local cop once too often. They escape, Filemon's mother gets kidnapped by Fredy and taken to Tirania. The spy is killed in Fredy's place as Fredy ingratiates himself with the President, while having Filemón's mother tortured. The heroes arrive and there is a big battle where Filemón is apparently killed. Then Mortadelo receives a mortal wound, but Filemón gives him a cup of water, which turns out to be the Holy Grail, Mortadelo drinks it and heals quickly, while Fredy gets his just deserts. Mortadelo and Filemón return home, their mission successfully accomplished.