Substitute Bride — Margery Scott

Six years after Cole Berringer goes west to build a new life, he writes to his childhood sweetheart, Sarah Main, and proposes marriage. But instead of the woman he left behind, her twin sister, Elizabeth, arrives in Colorado to take her place. Elizabeth Main has loved Cole for years, but has always known she isn't the woman he loves, so when her twin refuses his marriage proposal, she grabs at the chance to make her dreams come true. As the weeks go by, Cole and Elizabeth grow closer, and Elizabeth is convinced it's only a matter of time until Cole returns her love. But then, Sarah arrives …