It’s the night of Magical Mer-Moon, and Capt’n Turbot and Francois race out in their diving bell to capture images of the fabled Merpups! But when a sea slug decides their diving bell is a great place for a nap, it’s the Merpups who send for help, turning Marshall into a Merpup! Ryder and the Paw Patrol dive into action to save the Cap’n and Francois, and get Marshall back to dry land before he turns back into a pup!