Alien Offensive - Book 3 - Humankind Strikes Back. Alien Offensive, #3

In episodes one and two, a distant alien species whose home planet was in danger because of its failing red dwarf star, tried to eradicate all life on Earth and then terraform the planet to meet their needs. Thanks to the exceptional talents of two inspired physicist, who devised two unique weapons, each tailored to repel the desperate and repeated alien assaults, the world was spared not once, but twice.
Humankind celebrated their victories and felt safe from future aggressions, but those celebrations may have been premature. A renegade alien Commander, now repelled for the second time, and against the orders of his Elders, contrived plans to return to Earth with a world-destroying weapon of his own - this time determined to succeed .