The Eleventh Hour - All The Other Gods, #1

The past is always present. ?On a brisk summer's night, in a state of mundanes, a peculiar train leaves the station, its heading, a hidden borough of magic-and magicks. Hampshire, New York-a borough divided into three counties, each controlled by a magical noble family-Mandrake (County of Merlin), Dimitri (County of Morgana), and Bane (County of The Fates). After a treacherous plot unfolds, Alfred Mandrake, Head of the Mandrake family-who maintained decades of peace in Hampshire-is dead.
But when his eldest son plots to wage war against the family responsible, his sister Hermione intervenes. Hermione is a 21-year-old witch, and luckily, she was left her grandfather's final magical invention: a pocket watch that uses memories to travel back in time. With the trinket in her possession, Hermione and her half-brother intend to go back to March-four months before the massacre, that killed thousands, including their father. Unfortunately, when their plan goes awry, they land thirty years in the past, with the trinket suddenly inoperable.
Now, they must repair it, but navigating the past is no easy feat. As Hermione explores this dark, unfamiliar world, pursued by murderous villains, she soon learns to save her future, she may have to destroy her past.