Cinderella Boy by Kristina Meister

Sixteen-year-old Declan is the perfect son . . . except for one tiny issue. When his sister Delia comes home to find him trying on her clothes, he fears her judgment, but she only fears his fashion choices. One quick makeover later, Declan is transformed into Delia’s mysterious cousin Layla and dragged to the party of the year, hosted by Carter, the most popular boy in school.

When Carter meets Layla, he fumbles to charm her. He adores her sense of humor and her poise. But when she vanishes in the middle of the night, he’s left confused and determined to solve the mystery of who she is.