The Hourglass Door — Lisa Mangum

Abby's senior year of high school is going according to plan: good friends, cute boyfriend, and college applications in the mail. But when Dante Alexander, foreign-exchange student from Italy, steps into her life, he turns it upside down. He's mysterious, and interesting, and unlike anyone she's ever met before. Abby can't deny the growing attraction she feels for him. Nor can she deny the unusual things that seem to happen when Dante is around. Soon Abby finds herself drawn into a mystery whose roots reach into sixteenth-century Florence, and she uncovers a dangerous truth that threatens not only her future but the lives of those she loves.