False Colours is a Regency romance

Regency romance

Regency romances are a subgenre of romance novels set during the period of the British Regency or early 19th century. Rather than simply being versions of contemporary romance stories transported to a historical setting, Regency romances are a distinct genre with their own plot and stylistic...

 novel by Georgette Heyer

Georgette Heyer

Georgette Heyer was a British historical romance and detective fiction novelist. Her writing career began in 1921, when she turned a story for her younger brother into the novel The Black Moth. In 1925 Heyer married George Ronald Rougier, a mining engineer...

. Set in 1817, it concerns a young man temporarily impersonating his missing twin brother.

Plot summary

Kit Fancot returns home to England from diplomatic service in Vienna to find that his twin brother Evelyn has disappeared. Although this would not normally be a problem, Evelyn is supposed to meet the autocratic grandmother of the lady to whom he has proposed. Kit is obliged to impersonate his brother to save the betrothal.
When Evelyn doesn't reappear, Kit has to indefinitely stay in the appearance of Evelyn and decides to retire to his family home in the countryside. Evelyn's chosen lady, Cressy, comes with her grandmother to the Fancot family home however. By careful deduction Cressy is able to work out that Evelyn is actually Kit in disguise, but as they have fallen in love with each other, she helps him with the deception.
Eventually Evelyn comes home with a tale of what happened to him. He discloses that he met the lady of his dreams and Kit thinks up of a fantastical idea to make sure that both brothers can get what they wish without any scandal.