Five hundred years in the future, the Earth is dying, overrun with pollution that the Great Council refuses to stop. 16-year-old Tess is a proud Earther who wants to save the planet, but the government says that shipping all humans to Mars must happen for humankind to survive. Tess fears the day she gets drafted because no one ever hears back from the Red Planet. When Tess's turn comes to board a one-way ship, she discovers a horrible truth: an alien race has taken over the government and wants Earth for themselves. But Tess's horror has only begun. The settlements on Mars are harsh, where colonists struggle to survive. All Tess wants is to get back to her rightful home, but by running into Matthew, a fellow colonist with some secrets of his own, she gets wrapped up in a dangerous plan to do so: Mars must invade Earth. Tess has no choice but to face war, and perhaps even to question the identity she holds dear. 

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...