When small-town courtesan Emma Hart (Vivien Leigh) suddenly finds herself married to British Ambassador Sir William Hamilton (Alan Mowbray), her little world is turned upside down. Just as Emma is finally settling into her new life as the eponymous Lady Hamilton, she meets British naval hero Horatio Nelson (Laurence Olivier) and the two fall madly in love. However, their forbidden romance is soon threatened by the ever-growing shadow of the Napoleonic Wars.