Ashley decides to throw Mary-Kate a super surprise party for being the first student ever to get a perfect score on the statewide history exam. One problem: Mary-Kate is super-snoopy and impossible to surprise!

When Ashley decides to surprise Mary-Kate with a party, she wonders how she will keep it a secret from her seriously snoopy sister - until she hits on the perfect plan...

She will get Mary-Kate to help her create a surprise party for their friend Lavender. Mary-Kate is enthusiastic - picking out invitations and decorations for Lavender (whose taste is the total opposite of Mary-Kate's). Little does Mary-Kate know that she is, in fact, planning her own party!

But Mary-Kate is planning a party that is so not her! Can Ashley change everything around in time and save the party before Mary-Kate figures it out?