The Danék is a wild, treacherous river, and the Fobisher family has tended it for generations - clearing it of ice and weed, making sure boats can get through, and fishing corpses from its bleak depths.

Wulliam's father, the current Riverkeep, is proud of this work.

Wull dreads it. And in one week, when he comes of age, he will have to take over.

Then the unthinkable happens. While recovering a drowned man, Wull's father is pulled under - and when he emerges, he is no longer himself.

A dark spirit possesses him, devouring him from the inside.

In an instant, Wull is Riverkeep. And he must care for his father, too. When he hears that a cure for his father lurks in the belly of a great sea-dwelling beast known as the mormorach, he embarks on an epic journey down the river that his family has so long protected, but never explored.