An archaeological digrecovering a Celtic stone, a medieval shipwreck and careless talk by young archaeologist, Ben Harris, spark off a robbery on the Scottish Highland estate of Sir Ranald Sinclair, uncovering a treasure that has been hidden for centuries.The robbery follows the opening day of the grouse season, hence the title of the book. The chief villain, grail fanatic Russian Boris Zadarnov, also abducts Sir Ranalds wayward daughter, Fran, who is already in love with Ben. American oilman, Al Regan, leads a rescue party to Paris where Fran is freed and most of the treasure recovered, but the thieves escape with a ruby encrusted chalice.
For a series of misdemeanours, including failing to spot that the Celtic stone was a fake, Benis is sacked from his university job. He finds consolation in the arms of Fran and moves north to continue treasure hunting, making the discovery of his life near one of the ancient Sinclair castles. Has he found the greatest archaeological prize in Christendom, the Holy Grail? Will he be able to protect it from the malevolent attention of Alexei, younger brother of the deceased Boris?
The genre is mystery/suspense with a streak of romance running all the way through. The action takes place mainly in Caithness with forays to Edinburgh, France, Italy, Egypt and Poland.