A small mining town. A brutal double murder. A killer among them.

DS Lucas Walker is out bush with his little sister Grace from Boston. They're fetching his cousin Blair, who's been mining boulder opal in Kanpara. The town is tense with rumours of a big opal find, and Blair wants out.

But Kanpara is in Channel Country, and when the three try to leave the next day, they find themselves completely cut off. A deluge far north has flooded the rivers overnight, making the roads impassable. Then Blair receives a shocking phone call.

Two bodies have been found, brutally murdered.

Trapped, with a killer in their midst, Walker is in a race to uncover the murderer before the water recedes. And when Blair is arrested by local police, the stakes couldn't be higher. With all his focus on clearing his cousin's name, will Walker see how much danger his sister is in before it's too late?