Shelly and her merfriends are excited to sleep in the museum until they start to wonder if it's haunted in this spooky Mermaid Tales adventure. It's almost Shelly's birthday! She can't wait to have her friends over and eat her grandfather's homemade pizza. But when Pearl gets involved in the party planning, the ideas get out of hand. Soon Shelly's small sleepover turns into an overnight extravaganza at the People Museum, complete with a scavenger hunt and scary stories! Shelly's not so sure about spending the night in the museum with its dark spaces and creaking exhibits. But when the day arrives, everything goes swimmingly—that is, until strange, glowing lights start to appear. Could the People Museum be haunted? Or is something fishy going on?