Joan and the Selkie - Joan of Kerry, #4

No one visits a dragon's island uninvited. When Joan's dragon companion, Rory, discovers a mysterious satchel on his secret island off the coast of Ireland, they both know something feels amiss. And since the satchel holds a carefully folded selkie skin, that something promises to be bad. Selkies never leave their skins unattended. Not on purpose. Joan and Rory set out to uncover the secret of the abandoned selkie skin, a quest that brings them face to face with more of the mythical seal people.
And a tragedy that has cost lives. To save the day, Joan and Rory will have to face the dangers of the ocean deep. And they might just have to burn.