As they search for their missing father near their Cornwall home, Sapphy and her brother Conor learn about their family's connection to the domains of air and of water.

When she incurs Neptune's wrath by finding a diamond ring buried under rocks in the ocean, Emily is put under a curse that will force her to choose to be either a mermaid or a human and split up her parents forever.

Two children set out to capture a mermaid, but she manages to escape all of their traps.

Reunited with her merman father and now living on an island located in the Bermuda Triangle, twelve-year-old Emily accidentally awakens the fearsome kraken and also faces a bully from her past.

When her home is threatened by fire, Jessie returns to the magical world of the Realm and visits the mermaids of Under-Sea to search for a wish-stone.

"... One September evening in 1785, Jonah Hancock hears an urgent knocking on his front door near the docks of London. The captain of one of Jonah's trading vessels is waiting eagerly on the front step, bearing shocking news. On a voyage to the Far East, he sold the Jonah's ship for something rare and far more precious: a mermaid. Jonah is stunned--the object the captain presents him is brown and wizened, as small as an infant, with vicious teeth...