The Tide Lords Series

When a routine hanging goes wrong and a murderer somehow survives the noose, the man announces he is an immortal. And not just any immortal, but Cayal, the Immortal Prince, hero of legend, thought to be only a fictional character. To most he is a figure out of the Tide Lord Tarot, the only record left on Amyrantha of the mythical beings whom fable tells created the race of half-human, half-animal Crasii, a race of slaves.
Arkady Desean is an expert on the legends of the Tide Lords so at the request of the King's Spymaster, she is sent to interrogate this would-be immortal, hoping to prove he is a spy, or at the very least, a madman.
Though she is set the task of proving Cayal a liar, Arkady finds herself believing him, against her own good sense. And as she begins to truly believe in the Tide Lords, her own web of lies begins to unravel...