The Biritsh Ambassador in Naples (Alan Mowbray) marries the beautiful Emma (Vivien Leigh) who has a dark past in England. As Lady Hamilton she lives the high life, being friends with the King and Queen of Naples. She meets the the British naval hero Horatio Nelson and despite both of them being married they start a love affair that is only just tolerated by the establishment because of his military success against Napoleon. The film is dominated by the great performance of Vivien Leigh as Lady Hamilton as she plays a range of emotions as she comes to the realisation of her posiition as the beautiful mistress.