Jack and Annie travel in their magic tree house to the land of the mystical selkies to seek a magical sword for Merlin.

Aran has never truly fit in with his selkie clan. He was born in his human form, without a pelt to transform him into a sleek, strong seal. Each day he waits, left behind while his selkie family explores the deep ocean. What if his pelt never comes? Does the Moon even see him? Is he putting his clan at risk? When his mother undertakes a journey to the far north to seek help, Aran is left in the care of a reclusive human woman on remote Spindle Island....

"On remote Rollrock Island, men go to sea to make their livings--and to catch their wives. The witch Misskaella knows the way of drawing a girl from the heart of a seal, of luring the beauty out of the beast. And for a price a man may buy himself a lovely sea-wife. He may have and hold and keep her. And he will tell himself that he is her master. But from his first look into those wide, questioning, liquid eyes, he will be just as transformed as she....

Fifteen-year-old Jenn McDaniel's life on Whidbey Island becomes more complicated and her relationships with old and new friends take strange turns, partly due to the arrival of a woman researching a strange black seal.