What would you do if you were playing in a pick up Celtic band at an Irish pub in downtown Chicago and a biker man yanks you outside, bites you, says "welcome to the family" and then disappears into the Chicago River? If you are Conor Archer, you would be in pain, wondering what just happened, and then remembering that your mom is dying and you need to get home fast. He arrives in enough time to hold his dying mother. But she has time to tell him that he must go to Tinker's Grove, the hometown he has never seen. It is an old Irish immigrant town from the 19th century, by the banks of the Wisconsin River. Going there is the only way he can be healed.
He collapses when he arrives in the center of the town, seriously ill. He wakes up to Troubles, a chocolate Labrador, licking his face and a bunch of people standing around him who soon will be his friends. They want to take him down by the river where there is a Native American burial mound. They say he can be healed there. And that's when Conor realizes he is in a strange town with many mysteries and some really strange people.
Tinkers Grove holds secrets. There are the "dark ones", some of the children of the town, who have the powers of the wild animals of the forest. People talk of the river demon Piasa, a water wraith corrupting everything it touches. And they speak of someone or something that dwells in the Indian burial mound. He or it is mysterious and powerful, an immigrant like them from the Celtic lands beyond the sea, but the town knows that presence to be good, holding off that creeping evil. The people seem to think that Conor Archer is some savior in a coming battle between good and evil.
Believing this was all crazy talk, Conor ignores it till he starts changing, shape-shifting, becoming something other than human. No longer does he think the rumors just legend and fantasy. A gen-tech company comes to town wanting to do experiments on the "dark ones" and makes a devil's bargain with the ancient evil present in the river. Myth and science meet in a bargain of destruction and only Conor will be able to keep the horror from infecting the town and the land. A battle with an ancient evil for the future of the world is about to begin.