After serving with distinction in his Regiment with the Duke of Wellington, civilian life bores the handsome Marquis of Heroncourt and he fills his time with empty affaires de coeur that bore him even more. But when his demure, humbly-dressed but beautiful young neighbour Lady Mimosa Field arrives unannounced at his ancestral home, Heron Hall, to beg for his help, he is instantly intrigued. Mimosa’s villainous cousin, Norton Field, is plotting to murder her young brother, Jimmy, in order to inherit the title of the Earl of Petersfield and his valuable estate.