In the Earthfall Trilogy closer, Sam and his friends face the ultimate threat to humanity.Sam is still coping with the changes he began to experience in Retribution (2015), such as shape-shifting abilities and a new form as an Illuminate-human hybrid. He is almost ready to reveal his secret when something strange happens to the Sleepers, the mind-controlled humans that the resistance cares for and works to free, causing them agony. Then Sam collapses and wakes up in Scotland with his father, the dead Illuminate Suran, speaking in his head and leading him to the Illuminate ship, the Scythe. But it's not Suran—it's a digital ghost called the Construct that wants Sam to save the Heart, the data crystal where the consciousness of billions of Illuminates are stored, and defeat the Voidborn for good. Recaps on the Illuminate and Voidborn races and previous events slip into narration as unobtrusive and welcome reminders, and the action's nonstop as Sam and friends face new threats that may stop them from reaching the Illuminate consciousness and strategizing against the Voidborn's Primarch in the imminent battle for humanity. Heart-pounding action and alien technology descriptions are immersive fun, but they are anchored by the characters' genuine connections with one another, giving the story weight and stakes. The fast pace keeps readers skipping past any potential plot weaknesses, and the satisfying conclusion reveals the impact of the war's costs. Race factors in the story only as human, Illuminate, Voidborn, and hybrids.A popcorn-and-explosions finale well befitting the series. (Science fiction. 9-14)