Fantastic Four #221
Tower of Crystal... Dreams of Glass!
At the North Pole the Fantastic Four observe the crystalline structure Reed thinks is responsible for recent power blackouts and the threat to the Earth's magnetic field. As the structure is surrounded by hundreds of alien creatures, the task of further investigation falls to Sue.
In spite of being invisible, Sue manages to trip a perimeter alarm that alerts the aliens to her presence, and so Reed, Ben, and Johnny join the fray in the hope of distracting them while Sue completes her mission. Unfortunately, the aliens prove to be a composite being capable of splitting into apparently limitless, multiple versions of the same form or combining into a single huge mass, and they prove well-matched against the three members of the Fantastic Four. As Sue examines the crystal tower, she notices a hole in the ice and evidence of activity below the surface.
Descending through the ice hole she discovers an alien space ship and on entering is confronted by its inhabitants, three strange telepathic aliens. Their leader, Primus, explains that they hail from the Beta Lyrae system and have been stranded on Earth for half a million years since the Earth's electromagnetic field last reversed and rendered their ship incapable of flight, the three aliens having been in suspended animation while their mindless drones worked to find a way to reverse the EM flow.
Primus realizes that the inhabitants of Earth are now an advanced culture and that to continue their experiments would seriously endanger life on Earth, and so hostilities are ended. Reed helps the aliens repair their spaceship and the Fantastic Four prepare to return home, though not before Ben has demolished the crystal tower in his own inimitable fashion.
Recurring Characters
Fantastic Four (Mister Fantastic, Invisible Girl, Human Torch, Thing)
Continuity Notes
The alien race here is identified as the Flb'Dbi as revealed in Official Handbook of the Marvel Universe #3