1923: In his last years, Sherlock Holmes has abandoned his strict method of logic for the practice of spiritualism, to the everlasting shame of his old friend Dr. Watson. When Lord Carnarvon dies unexpectedly, barely two months after opening the tomb of Tutankhamun, Holmes blames his death--and a string of others, from an American millionaire to an Egyptian prince, on an ancient curse. But Watson, never one for the supernatural, decides to finally part ways with the formerly great detective.

However, shortly after his departure from Holmes, Lord Carnarvon's daughter, Lady Evelyn, approaches Watson with a plea: accompany Holmes to Tutankhamun's tomb to uncover the truth of her father's death, whether natural, supernatural, or cold-blooded murder. Watson reluctantly accepts the challenge. But much to his displeasure, there's a third member of their company--Mrs. Estelle Roberts, who communicates with the dead.

Although divided by different beliefs, the trio must band together to unravel the extraordinary secret of the boy king and the treasure missing from his tomb that men have killed for. Their journey takes them from London to Monte Carlo to Cairo and Luxor, and finally to the place that haunts Sherlock Holmes's dreams, the place he swore never to return to: the Reichenbach Falls, where the spirit of the one man he killed in his long career may be awaiting its revenge: Moriarty.