The Masqueraders by Georgette Heyer

In the glittering world of Georgian England, two siblings on the run hide behind daring disguises — Prudence as her brother and Robin as her sister — to escape the aftermath of a failed Jacobite rebellion. Their plan to blend into London society quickly entangles them in a web of duels, deception, and unexpected romance. When Prudence, posing as a gentleman, meets the gallant Sir Anthony Fanshawe, her carefully crafted disguise begins to unravel in ways she never imagined. The Masqueraders is a witty tale of courage, love, and audacious intrigue, where appearances deceive and hearts reveal the ultimate truth.