The Micronauts and the Coffin family fight a mad professor who build a Pit as a door for the Microverse.
Complete Summary (with Spoilers)
On Homeworld, Slug, leader of the underground movement is imprisoned in the body Banks of Baron Karza. But this one don't know who she is and watch at her like another pity prisoner of his Dog Soldiers while the young woman is trying to locate and liberate the Prince Argon . At this moment, the prince , transformed by Karza in a centaur, succeed to free by himself but the tyrant stop him in a few seconds, Unfortunately, Slug shows herself insulting the Baron and this one decides to give her beautiful body to a old duchess Belladonna., a faithful customer of the Body banks.
On Earth, In their flying vehicle (called astrostation), the micronauts search the brainwave patterns of their friends Bug. The signal leads them in front of the Human Engineering Life Laboratory, one building in the Cap Canaveral complex. That when they find Muffin, the cocker spaniel of the Coffin family, in a car. After liberate him, Mari enters in the Laboratory riding him (since all the Micronauts are a few inch tall). Her friends, them, have to enter by the ventilation shaft.
Deeper in the building, Ray Coffin and his son Steve discover that Philip Prometheus already knows the microverse. In his laboratory, a lot of specimen of Microverse inhabitants lie in jars and some print-out show Acroyear warriors and others Microverse species.
However, when Steve talks about Commander Rann and the Spacewall (see Micronauts #2 for their encounter), the professor Prometheus becomes excited and violent. Becoming half-human, half-machine in a space accident, he want to go in the Microverse for obtaining a more advanced science and transform himself as a god. It's the reason why he build the Prometheus Pit, some door for the Microverse. In order to keep the secret, he even build robots as his security guards.
But all this drives him insane and he starts to hurt Steve. So Bug, hidden in the laboratory, attacks the mad scientist. In the same time, Muffin and his rider, Marionette, enter in the room. The professor, excited by the discover of one more microverse specimen, active his Pit, trying to throw bug, Mari and Steve Coffin through it. Acroyear and Commander Rann come for helping their friends. They fight with the robot guards and Prometheus while bug helps Marionette to not be propel in the Pit and Microtron succeed to catch Steve with his telescopic arm. Finally, Ray Coffin, in order to save his son, drags Prometheus in the Pit and the two former astronauts disappear.
But the micronauts remain in front of the Robot guards with Steve to be protect.