Shadowfall (Immortals Descending #2)

It is said the demon in the well will give you your heart's desire...for a price.

When Declan's prince and best friend, Arwyn, goes seeking the demon for himself, he surprises Declan by leaping into the demon’s well. But when Declan pulls him out, it isn't Arwyn he rescued, but a demon wearing his skin. No one believes Declan that Arwyn's soul has been corrupted by the shadow in the well, and with Arwyn taking up arms against the king's fleet by becoming a pirate, all that matters is stopping him.

When Arwyn offers him a terrible bargain, Declan agrees, hoping it will finally give him the truth about what happened to his prince...and a chance to find the man he'd loved since childhood.

But Arwyn isn’t a demon. He’s a god, and he is very, very good at knowing what people really want. He is convinced that for Declan, it isn't the prince who went into the water that has captivated him...but the shadow that came out of it.