Hours after Holmes and Russell return from solving the murky riddle of The Moor, a bloodied but oddly familiar stranger pounds desperately on their front door, pleading for their help. When he recovers, he lays before them the story of the enigmatic Marsh Hughenfort, younger brother of the Duke of Beauville. Marsh has returned to England upon his brother's death, determined to learn the truth about the untimely death of the hall's expected heir—a puzzle he is convinced only Holmes and Russell can solve.

It's a mystery that begins during the Great War of 1918, when young Gabriel Hughenfort, the late Duke's only son, died amidst scandalous rumors that have haunted the family ever since. While Holmes heads to London to uncover the truth of Gabriel's war record, Russell joins an ill-fated shooting party. A missing diary, a purloined bundle of letters, and a trail of ominous clues comprise a mystery that will call for Holmes's cleverest disguises and Russell's most daring journeys into the unknown—from an English hamlet to the city of Paris to the wild prairie of the New World.

The trap is set, the game is afoot, but can they catch an elusive villain in the act of murder before they become his next victims?

At the close of the year 1918, forced to flee England's green and pleasant land, Mary Russell and Sherlock Holmes enter British-occupied Palestine under the auspices of Holmes' enigmatic brother, Mycroft. "Gentlemen, we are at your service." Thus Holmes greets the two travel-grimed Arab figures who receive them in the orange groves fringing the Holy Land.

Whatever role could the volatile Ali and the taciturn Mahmoud play in Mycroft's design for this land the British so recently wrested from the Turks? After passing a series of tests, Holmes and Russell learn their guides are engaged in a mission for His Majesty's Government, and disguise themselves as Bedouins—Russell as the beardless youth "Amir"—to join them in a stealthy reconnaissance through the dusty countryside.

A recent rash of murders seems unrelated to the growing tensions between Jew, Moslem, and Christian, yet Holmes is adamant that he must reconstruct the most recent one in the desert gully where it occurred. His singular findings will lead him and Russell through labyrinthine bazaars, verminous inns, cliff-hung monasteries—and into mortal danger.

When her mentor's inquiries jeopardize his life, Russell fearlessly wields a pistol and even assays the arts of seduction to save him. Bruised and bloodied, the pair ascend to the jewellike city of Jerusalem, where they will at last meet their adversary, whose lust for savagery and power could reduce the city's most ancient and sacred place to rubble and ignite this tinderbox of a land...

Classically Holmesian yet enchantingly fresh, sinuously plotted, with colorful characters and a dazzling historic ambience, O Jerusalem sweeps readers ever onward in the thrill of the chase.