The Admiral's Lady — Mary Ann Gibbs

Susanna Farebrother is eagerly awaiting her gala coming-out ball and the arrival of her Admiral father, who is due back from the sea.
The headstrong lovely eighteen-year-old has also fallen in love with a dashing army captain. But it is her neighbor, young Edward Royde, who really captures her attention. She hates him.

These romantic tangles are set aside when Admiral Sir John Farebrother arrives home, for Susanne senses something is very wrong. She soon discovers what is peculiar about her father's return. Papa is not Papa at all. It is his twin brother Will, who is masquerading as Sir John...