Fourth world

"Iamos, S.C.D. 8378. Nadin's planet is dying. As its atmosphere drains away, her people are forced to live huddled in domed cities for protection. With only enough resources to support the population for one more year, time is running out. Nadin thinks she's found a way to save Iamos, but it will mean defying the planet's rulers, the geroi--and betraying the geroi could cost her everything. When a strange boy from another world appears out of nowhere outside the citidome's glass walls, Nadin knows for sure that her plan will work. But to build the device that can save her people, Nadin must first find the legendary city of Elytherios. And to do that, she'll need the help of the mysterious alien boy named Isaak. Mars, 2073 C.E. All Isaak wanted was to get through his senior year at the Academy in one piece. Everything would have been fine if he hadn't found that ancient coin among his missing father's possessions. The coin seems to have a strange connection not only to Isaak's family, but to Mars' ancient past. But how is that possible, on a planet that was supposed to be dead until just forty years ago? Now Isaak's got agents of the Earth's government on his tail and a deranged factory worker stalking his every move. Everyone is desperate to get their hands on something called the Key. And the only way to escape is to unlock an even bigger secret, one that could change his life--and the fate of Mars--forever"--