The Unknown Quantity

From a Grand Master Award–winning author, a wife is drawn into her husband's business world of secrets and lies—and murder—in this thrilling mystery. Sarah Travers's husband Arthur asked her to meet him in San Francisco, where he's engaged in business related to his oil company, and is shocked to meet his newest employee. Lawyer Jake Dixon looks almost exactly like her husband. Arthur has been contracted by the government for covert work and hired Jake to impersonate him during his absence. He wants Sarah to go along with the deception by traveling with Jake back to their home in New York so that Arthur can complete his secret mission. But upon arrival, Sarah and Jake receive word that a dead body was found in San Francisco's Presidio Park believed to be Arthur. Fearing for their own lives, the couple continues to act as if Jake is Arthur, until they can learn the truth about the victim's identity. Then Sarah learns that someone has been threatening Arthur, someone dangerous enough to break into her home. And when the Travers's gardener is murdered, the police confront Sarah and uncover Jake's true identity. Now, they are murder suspects, accused of killing Arthur for his wealth. As Sarah and Jake fight to prove their innocence, they discover some unsettling truths about Arthur's business dealings and relationships . . . "One of Eberhart's most completely readable mysteries." —The New York Times

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Release date

Ebook: 13 January 2026