 Suffering from depression and nearing a breakdown, Holmes is accompanied by Watson to Cornwall for rest and recuperation as they tour the area s scenic coastal cliffs and Neolithic sites. The tranquility is interrupted by news that an unexplained tragedy has suddenly struck three siblings while playing cards in their home. The sister has apparently died from apoplexy, and her two brothers are suffering from acute dementia with expressions of fear and horror frozen on their faces. Showing great will power, Holmes discards his opium hypodermic and scrutinizes those involved in the case: an estranged third brother, the local vicar, and an enigmatic big game hunter and African explorer.