The Book of Hyrum. Return of the Wick Chronicles, #2

Hyrum Munson spent two years walking across Florida and Midlam for one reason: to deliver a message to his sister, the Queen of Pacifica: Daddy wants to kill Red and the Prince. He has no way of knowing that the war has been over nearly as long as he's been walking, or that Levi is long dead; he certainly has no way of knowing that his oldest brother is losing control over Florida's governing Quorum and nuclear war is looming.
Hyrum, an eight-year-old boy stuffed into the body of a 43-year-old man, only wants two things: to be good, and to remain in Pacifica. As Pacifica balances on the brink of nuclear war, Hyrum is stuck in the middle. If he goes home, he makes his mother happy and lives eternally as a little boy grown old, feared by his family. If he stays, he distances himself from the shadow of a life of abuse and has a chance at happiness.
Wick watches it unfolding, the people he loves forming a tight circle around Hyrum, the joy and wonder of his personality, and wants to know why his own family so afraid of him. The answer, he comes to see, is electrifying.