All the Butterflies in the World — Rodney Jones

With her senior year looming, Tess McKinnon has two goals: hanging out with her best friend, Liz, and avoiding her judgmental, alcoholic mother. Then yummy John Bartley arrives-to tell Mrs. McKinnon that her daughter is dead. Distinctly still alive, Tess is baffled by John's tales of 1800s time travel, rewritten lives, and love. She knows she's never seen him before, but her feelings refuse to be denied. When Tess and John discover an aged newspaper clipping that indicates John's uncle was hanged for Tess's murder in 1875, John decides to return to his time to save his uncle's life. Not really sure she even believes in this time travel stuff, Tess checks the article after John leaves. The words have changed, and she is horrified to find that John has been hanged instead. Armed with determination and modern ingenuity, Tess must abandon her past and risk her future for a chance to catch her own killer and find her first love for the second time.