Echo, Shelly Siren's best friend, is doing tail flips because she's going to see the hottest boy band around--The Rays! It's her classmate Pearl's birthday, and the Rays are going to perform at her exclusive party. Troublemaker Pearl has invited just about everyone--everyone, that is, except Shelly! Shelly urges Echo to go anyway, but Echo doesn't want to leave her friend out of the exciting celebration...so Shelly hatches a plan to make sure Echo sees her favorite group. And when the Rays do come to town (amidst plenty of under-the-sea, boy band drama), Echo returns the favor so that Shelly is included in the festivities--in the most unexpected of ways!