Nancy Springer 
Madbond 

A king and a madman in a dying world must join together, facing monsters and terrors to save what few mortals still remain, in the first book of the masterful Sea King Trilogy by one of fantasy fiction’s most accomplished world builders Once there were towering cities filled with masses of people. But no longer. Now six dwindling tribes huddle between the plains and the sea. Once the woodlands teemed with all manner of creatures—until the terrible Devourers swooped down from the skies to feed on them. Now all is silent.   Rad Korridun, king of the Seal Kindred tribe, seeks the answers that will save his people. To find them he must join with Dannoc, accused of foul murder and driven mad by the horrors he has witnessed but cannot remember. Kor and Dan are bonded together by a great and powerful magic, their minds and spirits and hearts united as one.   On their journey they join with Tassida—the tribeless wanderer and warrior, beautiful and mysterious. But what awaits them beyond the mountains is a darkness that dwarfs all nightmares as destiny draws them ever closer to the source of the end to all things.