Set in 1945, Best Kept Secret begins with a tied vote in the House of Lords over who should inherit the Barrington estate, leading to a pivotal decision by the Lord Chancellor that impacts the lives of Harry Clifton and Giles Barrington. As Harry promotes his latest novel in America, Emma searches for a mysterious girl found abandoned in her father's office on the night of his death. Meanwhile, Giles faces political challenges in defending his seat in the House of Commons, with his fate intertwined with that of Harry's son, Sebastian. Sebastian becomes entangled in an international art fraud involving a valuable Rodin statue, raising questions about his future and safety.