Carolyn Keene 
Slumber Party Secret [EPUB ebook] 

When her friend’s party is in jeopardy, Nancy takes the case!Rebecca Ramirez’s birthday is just two days away, and she’s having a slumber party. She made the invitations herself, with rainbow ribbon hair clips and everything. But now the invitations are gone. Somebody took them and the whole party is ruined. Or is it? Nancy Drew is on the case and maybe she can make sure Rebecca’s birthday is a party after all!