Mike Mars in Orbit - This is fourth in the series. Mike has been chosen out of the group of 7 astronauts of Project Quicksilver to be the first man to orbit Earth in a space capsule. All but one of his companions are as happy about this as Mike. The first sign of trouble comes with the discovery that a member of the press has located Skyhook and knows the general plan of Project Quicksilver. Then he meets up with his old enemy, Calhoun, and narrowly escapes an attempt on his life. And that is just a prelude to the peril that awaits him in outer space...