Timeless (Timeless #1)

the long version

When tragedy strikes Michele Windsor's family, she is forced to move from Los Angeles to New York City to live with the wealthy, aristocratic grandparents she has never met. In their historic Fifth Avenue mansion, filled with a century's worth of family secrets, Michele discovers the biggest family secret of all -- an ancestor's diary that, amazingly, has the power to send her back in time to 1910, the year it was written. There, at a glamorous high-society masquerade ball, Michele meets the young man with striking blue eyes who has haunted her dreams all her life. And she finds herself falling for him, and into an otherworldly romance. Soon Michele is leading a double life, struggling to balance her contemporary high school world with her escapes into the past. But when she stumbles upon a terrible discovery, she is propelled on a race through history to save the boy she loves -- and to complete a quest that will determine their fate.