In the last months of 1999 in Spokane, Washington, middle schooler Beverly Moody lives with her grandmother Gail, a USPS mail carrier.

With the reluctant help of unfriendly local record store owner Edward, aka "Anti", he puts the first song on tape for her.

In the search for the songs, Beverly forms friendships with Ellen, a Taiwanese transfer student and resident tough girl Nicky, mostly bonding over their shared interest in music.

The girls' developing friendship also includes creating music with Nicky's brother's band's instruments, inspired by the mixtape.

Initially the musician doesn't bother to really look, but when he does he recalls her as being a great lyricist but then dismisses her as a loser for having a baby and seemingly abandoning music.

The film ends with the three girls performing as Us Dudes R Sisters songs inspired by the mixtape, in a New Year's Eve party that includes their three families and Anti.