Repossession Of Earth

Returning from a visit of a distant alien planet on the other side of the galaxy, Colonel, Simon, Cooper, accompanied by his sidekick, Atom, discovers things have changed. He finds the Moon Base from where he'd departed, surprisingly abandoned with no indication where everyone went, and strong evidence it had been attacked by some superior alien invaders. He, also, discovers the Martian Terraforming operation, deserted, with indications it had been attacked by the same alien force.
When he eventually returns to Earth, he discovers the planet overrun by hard to kill, man-eating, beast, and sees how and why they were brought to his home world. Now, being the only possible salvation of humankind, Simon, has to make several complicated moves while seeking the assistance of other, willing and advanced, alien species.