The X-Men are being tossed around in the private jet as if they were in anti-gravity. Then, they are attacked by Lucifer with “a beam of pulsating light ”. Xavier follows the beam to Lucifer’s lair.
The beam also draws the attention of a group of ranchers from afar. They head towards the beam to investigate.
The X-Men trace the beam to the desert floor, and find some manmade geysers that erupt “opalescent gases”, designed to “shield something beneath them from detection from the air”. They spot a river nearby, which Xavier suspects to be the water source Lucifer needs to “operate those geysers ”. The river “disappears underground”, which the X-Men will use to trace the path back to Lucifer’s citadel.
The X-Men proceed on foot while Xavier remains behind with the jet. He will be monitoring them via “mental telepathy”.
Along the way though the canyon, the X-Men encounter the ranchers. They quickly take care of the ranchers and move on. At the river, Iceman creates a raft out of a block of ice so they can cruise down the river. They travel into a cavern where they are sucked into a whirlpool.
Meanwhile, Xavier is located by Lucifer and captured by robots.
Gifted with the power of flight, Angel is the only one who was able to escape the whirlpool. But he dives back into the vortex after his team mates. He spots only Cyclops and Marvel Girl, and helps pull them out of the river. Beast and Iceman are nowhere to be found. They come across an opening in the cave, but it is a trap.
Beast and Iceman emerge further down the river. They are attacked and hased by Lucifer’s robots. Soon, they are apprehended as well. Xavier is forced to witness the capture of his students.
Lucifer explains to Xavier his race’s grand design, “a weapon of indescribable potency ” called “Dominus”, and the myriad of robots created to operate Dominus. His race will use it to conquer the universe. They had already previously enslaved the “great and advanced civilisation” of “a planet of the star Sirius”.
Cyclops, Marvel Girl and Angel are trapped in a glass box. They are unable to break free or contact Xavier. Suddenly, the box opens and they feel themselves being sucked to the far end of the box by an “invisible force”. Iceman and Beast are tossed into the box with them. The X-Men are glad to be reunited.
Beast’s keen observations enables the X-Men to escape. He instructs Marvel Girl to flip the lever that the robot used to open the box. Cyclops “locate[s] a weak point on the robot’s back” and disables their prison guard. The X-Men make their escape, only to find themselves trapped in a maze.
With the X-Men freed, Xavier is able to contact them once again. He cautions them to be careful not to destroy anything, as they are within the “gigantic mechanical complex” that is Dominus. The X-Men find their way to the heart of the machine where they find Xavier and Lucifer.
Not heeding Xavier’s warnings, Angel intends to “[rip] everything up”. Cyclops stops Angel with an optic blast. Frustrated to see Cyclops had attacked Angel, Iceman hurls a large chunk of ice at the machine, to be stopped by Marvel Girl’s telekinesis. Cyclops explains to Iceman that he merely stunned Angel, and was following Xavier’s orders to ensure Dominus is not damaged. They are to concentrate on destroying the robots instead.
Lucifer’s robots finally catch up with the X-Men. But now the X-Men know how to defeat the robots and quickly destroy them.
Suddenly, Lucifer’s superior commands Lucifer from a “giant screen”. Lucifer has wasted precious resources; the robots needed to operate Dominus. Lucifer is thus “banished to a nameless dimension where neither time nor space exists”.
With the threat of Lucifer finally over, Xavier can finally explain to the X-Men that Dominus “would resist all [their] efforts to destroy it”. They would be wasting their energy. Destroying the robots on the other hand would render Dominus inoperable. While in close range of Lucifer, Xavier was also able to influence him to “command the robots too recklessly”. Victorious, the X-Men head home.
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