Molly, Gil and the Guppies must lead a baby dolphin named Buddy to his surprise birthday party.
Before Molly can introduce the show, she hears a strange noise. The noise turns out to be Gil, pumping up an inflatable dolphin. Gil jumps on top of the dolphin and pretends to ride it, but the pump comes loose and sends him flying as the air escapes! Gil finally lands and, with a deflated dolphin on his head, announces: "It's time for Bubble Guppies!"
On their way to school, Molly, Gil and Bubble Puppy spot some dolphins swimming close by a pier. As they watch, they are greeted by a friendly lobster, who loves taking pictures with his underwater camera. He introduces them to Buddy, a baby dolphin, whose first birthday is today! Gil and Molly can't wait to tell everybody about their new friend as they head to school. All of the guppies are excited when they hear, and Mr. Grouper gets the whole class thinking about dolphins. This inspires the Bubble Guppies to sing Hey Dolphin!
After the song, Oona tells the viewers that she's lost her star; the hair ornament she's never seen without! To find it, she visits Deema's "Lost and Sound". Deema suspects that Oona's star might be in the warehouse, but it's much too dark to see. Deema explains that they can use a dolphin, with its 'echolocation' skills to explore in the dark. The viewers are asked to help identify objects in the dark and, before long, Oona is reunited with her star! Mr. Grouper then announces that it's lunchtime. Lunch joke: sandwich and tail mix.
Molly tells the viewers more about dolphins, whilst Gil attempts to teach the little fish how to speak like dolphins. Unfortunately, the last little fish takes Gil's instructions to 'say hello' a bit too literally, and soon they're all at it as Gil chases them! Oona and Molly invite the viewers into the classroom where everyone is learning about dolphins. In the classroom, Goby, Deema and Oona make Buddy a birthday card whilst Mr. Grouper and the rest of the guppies find out that there are many different types of dolphin. They also find out that dolphins love to eat fish, something which concerns Mr. Grouper. Goby goes on to tease Mr. Grouper by pretending to be a shark, scaring him even more! It's then time to go outside.
Deema and Molly pretend to be submarine sailors, who also sell
ice cream to their underwater customers. Italian ice cream, of course. The ice cream sailors soon find their first dolphin customers, but before they can sell their first scoop, a tiger shark appears and scares everyone away! Deema and Molly rush to another location, finding some more dolphins But once again, the tiger shark appears! After losing the tiger shark again, Deema and Molly find some more customers, and ask the viewers to help them choose the right number of scoops to use. The tiger shark appears once more, but Deema and Molly discover that all he wanted was one of their ice creams. They gladly serve him some ice cream and they all lived happily ever after! Gil then invites everybody to do The Diving Dolphin Dance
After the dance, Gil is seen warning his 'dolphins' about fishing nets, and how they should be careful around them. However, Gil's attempts to warn the little fish end up with him getting tangled in the net! Molly is then greeted by Buddy and the lobster from earlier, who tells the Bubble Guppies that a special surprise is waiting for Buddy at his home!
All the Bubble Guppies follow an excited Buddy all the way to his home, but something is not right; all of the lights are switched off! Deema discovers that the light switch is broken, and they have no other way to see. Molly and Gil then remember that Buddy can use echolocation to find things in the dark. With the guppy's help, Buddy finds a party hat, a present and a birthday cake. Buddy's surprise is a birthday party, and everyone is there! Oona gives Buddy the card they made him and they all sing "For he's a jolly good dolphin!"
Just before the show closes, Gil attempts to use echolocation, just like Buddy did, despite Molly telling him that only dolphins have that skill. Instead of finding the little fish, Gil comes face to face with the tiger shark! Everybody laughs as the show ends.