False Colours by Georgette Heyer was first published in 1963.

Kit and Evelyn Fancot are identical male twins whose lives have gone in different directions with Kit going into the diplomatic service and Evelyn into the army. Evelyn, the eldest and therefore the inheritor of the family estate is about to announce his engagement to wealthy heiress Cressy Stavely, but Evelyn is missing from home and nowhere to be found, his mother Lady Denham is distraught. She is recently widowed and is mired in debt, and she still can’t stop spending money. It’s important that Evelyn’s marriage goes ahead, but all depends on the elderly Lady Stavely, Cressy’s grandmother, and she’s notoriously difficult.

When Kit arrives home after being away for a few years he feels that something has happened to Evelyn, he’s worried about him too.

Few people are able to tell the difference between the twins, so their mother persuades Kit to pose as Evelyn at the family gathering, he’s not keen to do it but everything goes well, too well in fact!

This Regency romance hit the spot for me, it was just what I needed after reading a few quite bleak books prior to this one. It’s absolutely chock-full of Georgian slang, I looked some of it up in the dictionary as I’m always in doubt as to whether she has just made it all up, but every time I do that the phrase is actually in the dictionary, she certainly did her research!