When a selkie's Coat trades white for silver and black, it's time to enter adulthood. They do this by roaming the ocean alone for two years - just them, an eternity of saltwater, and mortality staring them in the face. Ten percent of them die. The other ninety percent learn some heard truths about who they are, and which parts of themselves aren't worth sacrificing to survive.
Brielle is a week into hers when she finds a merman on the continental shelf. He's weird and dying; she's bored. So even though he's quadruple her size - and despite centuries of their respective species fighting like seagulls at a picnic - she decides to help.
Then sharks try to eat them both, Brielle gets kidnapped, the merman might not be a merman at all, and the Vedava - a race of demons that were stopped last time at the cost of the pantheon's strongest goddess - have escaped to poison the ocean anew.
