When the body of a young woman is found floating in a backwater of Wiltshire’s River Avon it appears she has drowned. But the deadly nerve agent found in her system points to a much more sinister end - and more deaths will follow. Under the long shadow of the 2018 Salisbury poisonings, DI Kate Sparrow must hunt a callous killer armed with a deadly toxin known as R.I.P. And if this wasn’t tough enough, Kate must also deal with her imprisoned sister - a psychopathic murderer who has a grim hold over her life. Meanwhile artist and dowser Lucas Henry is reluctantly pressed into helping a dying woman find her daughter. Which brings him crashing back into Kate Sparrow’s life once more - whether she likes it or not.