When Martin Strickland, a local farmer is found dead in his own woods; covered by truffle oil and mauled to death by a wild boar, the investigation leads DCI Barnaby to Wyvern House, a posh picturesque country house restaurant run by a tyrannical celebrity chef, Ruth Cameron. But soon, another murder occurs and this time, the poison spreads further than the intended target.

DCI Barnaby and DS Nelson join forces with two female Danish police detectives when the boss of Calder's Biscuit Company is poisoned in Copenhagen after opening an empty tin of his company's famous Golden Clusters.