"Adam has been a unicorn activist for four years and an honest to god recording artist for eight months when he goes to throw his trash in the dumpster one night and finds a baby unicorn hiding behind the recycling bin."

Sheriff Stilinski and his wife couldn't have children. In her desperation, Mrs. Stilinski found a young Selkie boy and hid his sealskin. Only she knew where it was hidden; when she died, so did that knowledge. Stiles grew to love his human family as his own, even grieving the death of his captor/mom, but the sea still calls to him in Beacon Hills.

When Kaz explained the mission to her, he'd described a deep-sea fish whose scales could reverse the harmful, out of control magic that was razing the streets of Ketterdam. No one had expected to find this, a half-dead, half-Siren Shu floating in the depths of a ship.