The Daring Twin by Donna Fletcher

When Fiona of the MacElder clan is told that she must wed Tarr of Hellewyk so the two clans can unite, she is furious that she has to marry a man she does not love. Fortunately, Fiona’s identical twin sister Aliss also cannot imagine a worse fate than a forced marriage and the two boldly concoct an outlandish scheme –– to become indistinguishable to the groom –– and it works.

Tarr, frustrated that he cannot tell the difference between Fiona and Aliss, nevertheless finds himself drawn to a particular twin. Unfortunately, as soon it becomes clear to him that Fiona is the one who has captured his heart, Tarr must battle with an unexpected enemy to keep his newfound love.