Debbie is in love with her best friend, Lisa. Enough in love that she frequently attends Christian Youth Group sessions where they constantly harp on the dangers of homosexuality, just to spend more time with her. It doesn't stop there. Debbie never swears, attempts to block out all improper thoughts, and only watches good old-fashioned family TV (i.e. Full House - this book is so full of Full House references that it is a 90s nostalgia fanatic's dream), because that's how wholesome Lisa lives her life. But Debbie's lesbian secret is discovered and her life spirals out of control as she attempts to tell Lisa before someone else can. During her journey, she relies on her new friends Tim and Emma and their invented religion, Bluedaism, to help build an identity separate from Lisa's.
I would say that Sparks is like a middle school LGBT version of Nick and Norah's Infinite Playlist. It's a novel about self-discovery, love, and friendship, and it all takes place in one night. It's definitely entertaining in its approach, but I think tweens would appreciate it more for its approach to identity through Bluedaism (especially the bits about being Blueish and patting Bluedha) than the LGBT factor. While S.J. Adams' novel focuses on gay acceptance and redefining what is "normal", the focus is more on accepting your personal identity. Not only does Debbie need to construct her own self, but Emma struggles to accept her weight, Tim struggles to reveal his true sexuality (straight) and characters are frequently forced into roles they don't fit. There is religious commentary sprinkled throughout. It's definitely not an attack on religion, but a discussion on how religion should compliment who you are, not force you to hide your identity.