Atomic sulfate is a lotion that, according to Professor Bacterio, eliminates pests from the field. However, the lotion does just the opposite effect: it enlarges animals, making it a serious danger to humanity.

The worst of the case is that one of the jars containing that compound was stolen by agents of the Republic of Tyranny. There the dictator Bruteztrausen governs, who tries to dominate the world. Mortadelo and Filemón's mission is to go to Tyranny and retrieve the bottle.