The third book in the Mary Russell-Sherlock Holmes series.
It is 1923. Mary Russell Holmes and her husband, the retired Sherlock Holmes, are enjoying the summer together on their Sussex estate when they are visited by an old friend, Miss Dorothy Ruskin, an archeologist just returned from Palestine. She leaves in their protection an ancient manuscript which seems to hint at the possibility that Mary Magdalene was an apostle—an artifact

...

In 1919, Sherlock Holmes and his future wife Mary Russell are smuggled into Palestine under cover of darkness. Disguised as Arabs they foil a Turkish plot to regain control of Jerusalem from the British.

Twenty years after he solved the case of the hound of the Baskervilles, Sherlock Holmes returns to Dartmoor to investigate a murder and another sighting of the hound. On this occasion he is accompanied by his wife, Mary Russell, who narrates.

Becoming bored with family life, Mary Russell follows Sherlock Holmes to London, where she meets a former Oxford classmate and becomes involved in a mystery that places her in a collaboration with Holmes.

"Mary Russell and Sherlock Holmes, hoping for a respite in the French countryside, are instead caught up in a case that turns both bewildering and intensely personal After their recent adventures in Transylvania, Russell and Holmes look forward to spending time with Holmes' son, the famous artist Damian Adler, and his family. But when they arrive at Damian's house, they discover that the Adlers have fled from a mysterious threat. Holmes rushes after...

"A queen, a castle, a dark and ageless threat--all await Mary Russell and Sherlock Holmes in this chilling new adventure. The queen is Marie of Roumania: the doubly royal granddaughter to Victoria, Empress of the British Empire, and Alexander II, Tsar of Russia. A famous beauty who was married at seventeen into Roumania's young dynasty, Marie had beguiled the Paris Peace Conference into returning her adopted country's long-lost provinces, single-handedly...