Kitty Trapp doesn't care that her twin sister is wedding first, or that Bitty gets the inheritance, or that her mother always favored Bitty more--but she is secretly devastated that Bitty doesn't seem to realize just how handsome and wonderful her bridegroom truly is. When Bitty panics and can't go through with the ceremony, Kitty tells herself she is taking her sister's place to save the family from scandal.
If she looked a bit deeper--and wedding a serious, honorable, distant man like Alfred Knight should make any woman look deeper--she might have noticed that she was a little bit in love with her sister's fiance.
And if she'd thought about it for more than a minute, she might have realized that switching sisters at the altar would bring about far more scandal than simply canceling a wedding.
Then again, Kitty had never been one to think things through...