Amanda Lemon (Mary-Kate Olsen) is a streetwise orphan who has only one person who really cares for her; Diane, (Kirsty Alley) her case worker at the orphanage. Alyssa Callaway (Ashley Olsen) lives with her father, Roger (Steve Guttenberg) a fabulously successful businessman who has buried himself in his work since his wife died several years ago. So, Amanda and Alyssa, are two girls from totally different backgrounds, but who look like identical twins. When they meet by chance, they realise they have more in common than just looks and decide to manipulate Roger and Diane into marrying. The trouble is, that Roger had plans to marry the snooty socialite, Clarice Kensington in one day's time, that's twenty four hours for the girls to use their likeness to turn the best laid plans of a group of grown ups into chaos.