Professor Bacterio has developed an elixir meant to stimulate a person's subconscious alter ego, and decided to test it on himself first.
The elixir works, but Bacterio's hidden persona turns out to be a vicious prankster who commits a lot of mischief all over town and then proudly calls El Super to inform him of his achievements.
headquarters in disguise and playing his jokes on Mortadelo, Filemon, and El Super themselves, but in the course of that action he gets knocked on the head and comes back to his senses.
Relieved that their ordeal is over, Mortadelo and Filemon take a sip of cognac to ease their nerves, but the bottle they drink from actually contains the rest of Bacterio's elixir.
As a result, they turn into villainous pranksters as well, and El Super and Bacterio end up as their first victims, rolling to the edge of a ravine inside a thoroughly sealed and disabled car.