Shelly Siren and her friends visit King Neptune’s royal castle and attend their first ball in this Mermaid Tales adventure. Shelly, Echo, Kiki, and Pearl are spending their school vacation at Neptune’s castle! Shelly’s aunt, Queen Edwina, has invited the girls to stay for a whole week, and while they’re there the girls can’t wait to visit the Royal Orca Museum, see the Palace Library, ride seahorses, and maybe even attend a royal ball. Shelly is nervous about meeting her royal family, especially since she’s never felt like a princess. But when she arrives at the castle, she is welcomed with curtsies, bows, and sea flowers. Queen Edwina even gives Shelly a sparkling tiara that she once wore as a young princess. Just as Shelly starts to relax and have fun, the tiara disappears and the girls have to find it before the queen finds out! The mergirls have a real mermystery on their fins! But will they be able to figure out who took the tiara before Shelly’s royal visit turns into a royal disaster?