As Princess Luna’s youngest daughter, free spirited, freshly minted college dropout Princess Cassiopeia constantly feels overshadowed by her beautiful older sister, Neoma, and is still unsure about her place in the world. She often gets into trouble by constantly defying Luna and pushing every boundary that stands in her way.

As the royals gather in Silver Shoals for the summer, Cassie revels in the recklessness and freedom of the ocean, finding friendship in dolphins and other sea creatures. She has formed a uniquely close bond with a particularly special dolphin, and she often escapes to the sea when she needs to clear her head. Cassie’s life becomes more confusing when she discovers that she has a very special gift: The ability to summon sea creatures.

As she tries to figure out how to use her newfound power to benefit Equestria, Cassie must also navigate her complicated relationship with Neoma, though the two sisters are completely different in many ways.

Dutiful, serious, steady, and dedicated to her role as a princess, Neoma often becomes frustrated with Cassie's wild personality. The two sisters have grown apart since Neoma became a wife and mother. They fight constantly throughout the summer, but Cassie still hopes they can heal their fragile relationship as Neoma struggles to come to terms with her failing marriage.

This trip will open fresh wounds, and healing may come from an unexpected source.