Asteroid Man

Jonga and Krull had a routine job in the solar system defence organisation. Week after week and year after year they checked the asteroids. 23rd century astronomy had accurately charted 2,812 of those miniature worlds, compared with the 1,539 that are known to-day.
Suddenly a new asteroid appears, and a survey expedition under Squadron-leader Gregg Masterson, is sent out to investigate. They expedition fails to return, and when the watching asteroid observation corps make another anxious check, they find that the mysterious planetoid has disappeared as mysteriously as it came. A second expedition is launched under General Rotherson himself. An expedition that finds the wreckage of the survey ships, and the bodies of every man except Gregg Masterson.
Where is the missing Squadron leader?
Who is the terrible ageless asteroid man? So strong that he can control the destinies of a planet. What is the beautiful Princess Astra of Altain doing in the labyrinth below the surface of the asteroid?