Years ago, the magnificent dragon queen Tintaglia forged a bargain with the inhabitants of the treacherous Rain Wilds. In exchange for her protection against enemy invaders, the humans promised to protect an unhatched brood of dragons. But when the dragons emerged as weak and misshapen hatchlings unable to fend for themselves, dragonkind seemed doomed to extinction. When even Tintaglia deserted the crippled young dragons, the Rain Wilders abandoned the burden of caring for the destructive and ravenous creatures. They were banished to a dangerous and grueling journey in search of their ancient dragon homeland, the lost city of Kelsingra, accompanied by a band of young and inexperienced human keepers, also deemed damaged and disposable.

Against all odds they have found the fabled city, yet myriad challenges remain. Sintara, Mercor, Heeby, Relpda, and the rest of the dragons struggle to find their wings—and their independence. Their human escorts, too, must contend with unsettling upheaval: Thymara, Tats, Rapskal, Sedric, and the others are transforming into Elderlings—true dragon companions. As old rules give way to new alliances, secret fears, and adult desires, the keepers must redefine their lives as they attempt to reawaken Kelsingra to its former glory. But gaps in the dragons' memories leave them all struggling to recover the magic that once animated the great city.

As the young Elderlings risk "memory walking" in the city's hidden history, an outside threat is growing. The Duke of Chalced has dispatched his forces to the Rain Wilds with a compelling mission: slaughter the dragons in an attempt to stave off his own demise. The tide of history is about to turn on a life-and-death battle that will ultimately decide the dragons' fate. If they win, the regal serpents will rule the world once more. And if they lose, they will vanish from the world forever.