The Otherwhere Post

Seven years ago, Maeve Abenthy lost everything: her world, her father, even her name. Desperate to escape the stain of her father's crimes, she lives under a fake name, never staying in one place long enough to put down roots.
Then she receives a mysterious letter with four impossible words: Your father was innocent.
To uncover the truth, she poses as an apprentice for the Otherwhere Post, where she'll be trained in the art of scriptomancy-the dangerous magic that allows couriers to enchant letters and deliver them to other worlds. But looking into her father's past draws more attention than she'd planned.
Her secretive, infuriatingly handsome mentor knows she's lying about her identity, and time is running out to convince him to trust her. Worse, she begins to receive threatening letters, warning her to drop her investigation-or else. For Maeve to unravel the mystery of what happened seven years ago, she may have to forfeit her life.