In grade school, Kate, Sarah and Rebecca discovered they were best friends. In seventh grade, they discovered makeup and began a diary of their important moments, "signed" in their own shade of lipstick. In high school, they discovered boys. Now the three are staring their thirtieth birthdays right in the face and determined to do something about where their lives are going. From mothers who gripe about their unmarried state to bosses who don't take them seriously, to ticking biological clocks - the girls don't want to care what others think but are tired of being seen as those almost-thirty-something singles. When an unwanted and definitely unexpected wedding invitation arrives, it sends the three of them on an adventure to save the blushing bride from the biggest mistake of her life. Using tests taught to them by Kate's great-grandmother, they begin a wacky search for the perfect man. But even if one of them finds love, will the man be able to live up to the strict qualifications in the lipstick diaries?