Invaded - Homeworld Trilogy, #2

The war between Earth and Mars has begun... After learning that an alien race-the Grounders-now control Earth and wants to take the planet for itself by shipping all humans to Mars, Tess and her new friend, Matt, are in trouble. They're the first wave of an invasion from the Mars colonies, and they might be the only hope of taking Earth back from the Grounders. Worse, Tess's parents have been kidnapped by the aliens, and not all humans are bent on helping them take down the Grounders.
It's up to them to march to the Grounder HQ in a machine that looks eerily like a tripod. But Tess knows who she is: a strong Earther, with a mission to save the Earth. She must fight the alien invasion in any way she can. Matt has brought her a purpose, and she's going to roll with it-even if the Grounders are armed with deadly weapons and outnumber them a hundred to one. But the biggest danger to Tess may not be the Grounders themselves, but a new revelation that will unravel everything she thought she knew.
There is no telling what Tess will do next...or what she will become.