The story opens in Constantinople during the sacred month of Ramadan, where Paul Patoff, a young Russian diplomat, and his impulsive elder brother Alexander are visiting. Alexander is reckless and arrogant, and he immediately becomes infatuated with a mysterious woman wearing an opaque yashmak who is accompanied by a menacing African attendant. Despite Paul's warnings, Alexander's persistent pursuit leads to a violent street encounter with the attendant, causing grave anxiety for Paul, who fears his career will be ruined by his brother's foolishness.
While visiting the magnificent mosque of Sophia at night to witness the solemn and overwhelming religious devotions of the faithful, Alexander suddenly vanishes. Paul and their official escort search the vast building and the twisting, lantern-lit streets of Stamboul throughout the night, finding no trace of the missing man. The search extends over weeks, but Alexander has disappeared as completely as if he had vanished into the waters of the Bosphorus.
Fearing accusations and whispered rumors of fratricide among the diplomatic circles, Paul is eventually sent away by his ambassador to visit his ailing mother in the Swabian Black Forest. Madame Patoff is staying at Teinach under the care of a neurological specialist named Professor Cutter. When Paul arrives to tell her the true story of Alexander's disappearance, she flies into a frantic rage and accuses him directly of murdering his favorite son.
Following this agonizing interview, Madame Patoff attempts suicide by throwing herself from a balcony over a sheer cliff at Weissenstein, but her fall is miraculously broken by the branches of a wild cherry tree. She is rescued by an American traveler named Paul Griggs, and her mind sinks into a strange, silent apathy from which she refuses to emerge, though she retains her outward dignity and physical health.
The narrative shifts to England at Carvel Place, the country estate of John Carvel, who has married Madame Patoff's sister. Here, Professor Cutter brings the silent and unrecognizing mother to live under secret care. Paul Patoff eventually arrives at the estate to visit his English relatives, where he meets Paul Griggs and his cousin Hermione. The tension thickens as the family struggles with the dark legacy of the past, while the enigmatic Madame Patoff remains locked away in her walled garden, guarding the secret of her broken mind.
