"Gillbert is a little merman prince, son of King Nauticus, the ruler of the seven seas. Gillbert has a really big little sister named Matilda--who comes from the aquatic part of outer space, a mermaid friend named Anne Phibian, and a little turtle best buddy named Sherbert. Today is a big day for Gillbert and friends. It's Everything Day and anything can happen on Everything Day! And if the prophecy is true, the Gogo-Gygoontah Fish could awaken and wreak havoc and destruction for all who make eye contact. Also: Gillbert goes to the surface to meet some (mostly) humans who are having a haunting time celebrating their Anything Day! And everything can happen on Anything Day! This will be a day to remember for Gillbert and his friends!"--Back cover.