Lewis Romayne returns to the family home, Vange Abbey, after a fatal duel in France–the memory of which still haunts him. In an attempt to put the experience behind him, he visits London where he meets Stella Eynecourt, who will become his wife. However, Romayne also comes across the cunning Father Benwell, who is determined to convert him to Catholicism and to regain Vange Abbey for the Church.

Romance blossoms when Catherine, a 47-year-old widow, and the 25-year-old Christopher meet at repeated performances of a poorly attended play. However, 1920s London society is shocked by such a match, its disapproval shared by Catherine’s daughter and son-in-law, the curate Stephen. As events unfold, can their relationship survive the opprobrium of those around them as well as the disparity in their ages?

Overcome with grief at her husband’s death, Lady Franklin, an eligible young widow, unburdens herself to Leadbitter–a gallant, hard-bitten ex-soldier who has invested his savings in the car he drives for hire–as he takes her on a series of journeys. He in turn beguiles her with stories of his non-existent wife and children, drawing her out of her self-absorption and weaving a dream-life with Lady Franklin at its heart.

A masterful blend of Gothic drama and romance, Wilkie Collins' mystery novel is an exploration of illegitimacy and inheritance. Set in Cornwall, the plot foreshadows The Woman in White with its themes of doubtful identity and deception and involves a broad array of characters. The "secret" of the book's title is the true parentage of the book's heroine, Rosamond Treverton, which has been written down and kept in an unused room at Porthgenna Tower. This is where, 20 years later, much of the novel's action is set.

Richard Mardick is an elderly man with a secret that he has kept since his youth. He recounts his memories to his young protégé and secretary so that his story can be preserved. Faced with illness, the teenage Richard was sent to live with different relatives while being trained as a farmer. Lonely and stifled by family life, he then met a girl and his life changed… with shattering significance for his future.