Loose cannon

Skyripper: "A Soviet scientist wants to defect because aliens nobody else believes in are planning to invade Earth. Tom Kelly is in Algiers to arrange his defection. If aliens get in his way he'll kill them just as quickly as he would anybody else." -- Page [4] cover.

Fortress: "America has built a huge orbital weapons platform to defend itself against enemies on Earth, but now there's evidence of aliens. Tom Kelly has been tasked to learn what they're doing here, even if that means leaving a trail of blood from Capitol Hill to the eastern borders of Turkey--and on into orbit!" -- Page [4] cover.