A sleepy Princess in Black takes a much-needed vacation and rides her bicycle to the seaside, where she plans to nap in a hammock, but her peace is disrupted by a roaring sea monster.

Noseholes and elephants! A pet-eating monster interrupts a perfect playdate with Princess Sneezewort . . . but who is that new masked avenger? Princess Magnolia and Princess Sneezewort have plans . . . mysterious plans, like a princess playdate! They dress-up slam! They karaoke jam! They playhouse romp and snack-time stomp! But then a shout from outside Princess Sneezewort's castle interrupts their fun. It's a monster trying to eat someone's kitty!...

"The Princess in Black and her friends are enjoying a day of sun and sea on Princess Sneezewort's royal boat when a real, live mermaid princess emerges from the waves! Eeeeeee! Princess Posy needs their help protecting her very cute sea goats from being eaten by a very greedy kraken. But the princesses and the Goat Avenger quickly realize that fighting underwater can be tough for land dwellers, and only the mermaid Princess Posy can save the day....