A small mining community. A murderer at large. And a flood that has trapped them all.

DS Lucas Walker is off duty. His young half-sister Grace is visiting from Boston, and he's supposed to be spending time with her at his home in Caloodie in outback Queensland. But instead they've driven 400 kilometres west to the tiny mining town of Kanpara to pick up Walker's cousin Blair, who's been digging for boulder opals and is suddenly very keen to get out. It's not like Blair to quit so easily. Walker has the definite sense that something is off.

On their arrival, the atmosphere is already tense with rumours of a life-changing opal discovery. The following day, they awake to find that Kanpara has been completely cut off by a flood and the roads will be closed for days. As they take in their predicament, Blair receives a shocking phone call.

A man and a woman have been found brutally murdered.