Finn is furious when his parents take off on another scientific mission to the other side of the world, and he has to stay with his grandmother on her farm. Not only are the kids at school less than welcoming, he also has to deal with his cantankerous great-grandfather who doesn't seem to want him around.

The Red River flowing by their property is the only thing that provides him peace – and a weird friend, the mysterious Angus, who teaches him to fish. But the river isn't always so placid – it's flooded before, and as the spring of 1997 arrives, it threatens to do so again.

As the floodwaters rise, Finn must work with his family and the community to face a monstrous adversary. Will the river once more endanger everyone's homes and livelihood? Can the challenge of fighting it bring the family closer together at last? And just who is Angus and what's his link to the river?