Still traveling with Scoot and looking for Flo's home beach, Splash recalls hearing about a beautiful reef nearby - perhaps that's where Flo's home is. They're all surprised when the once lush reef turns out to have become a ghost reef. Splash and friends, as Reeftown Rangers, stay to help the one remaining Parrotfish save the reef, realizing that if harm can come to this reef, it can happen to any reef, including Reeftown. / Splash and his friends end their journey, returning home to Reeftown, where they are delighted to see that Splash now knows that although there are fun adventures to be found all over their "One Big Ocean," Reeftown is home to him.

Splash and Bubbles have an argument and decide not to play together for a while. With the help of Dunk and Ripple, they learn how much better things go for each of them when they communicate and cooperate. Splash's friends think he is so good at hide and seek that they decide to challenge him to find sea creatures who can blend into the background, making them very hard to find.

When Splash and the others want to play with Dorsal, he tells them that first he needs to do his "job," which that day is using his echolocation to help his group find food. Splash and the others wonder if they need "jobs" to do in Reeftown and try to figure out what those would be. / To honor his talented Reeftown friends, Splash creates a talent show for everyone to show off their abilities. Splash then laments that he's got so many talented friends, but he has no talent to show. His friends remind him that his talent is making friends and organizing events like the talent show.

After the kids hunt for treasure and compare what they've found, Flo explains that she knows the location of a wonderful treasure that came from above the surface. Since the kids want to find it, Flo sets them out on a mysterious journey and if they follow her directions, the treasure will be waiting for them. / Bubbles, feeling self-conscious about a healing blemish on her face, meets Myshell, a friendly, outgoing decorator crab who has covered her shell with all kinds of shells, coral and sponges. Myshell teaches Bubbles how to feel good about herself from the inside out.

Dunk's cousin Mo comes to visit everyone in the reef, because he has a sunburn from spending too much time sunning himself above the surface. Looking to get as far away from the warmth of the sun as possible, the kids take Mo down to the Arctic, but he quickly realizes it is too cold for him there. / Splash and friends are having a great time pretending to be different fish, but Finny isn't good at pretending she is a fin whale because she is not used to using her imagination. Together, the kids teach Finny how to have fun harnessing the power of her imagination, while also learning about fin whales.

Bubbles learns that every drop of ocean water is full of life, and decides to take in a nanoplankton friend who is invisible to everyone, including her. / Tidy meticulously cleans up the kelp forest in anticipation of the arrival of his new partner, a female garibaldi fish named Neat. Splash and his friends, however, get Mrs. Tidy mixed up with another fish, who's not an easy fit in the kelp forest. When the real Mrs. Tidy (Neat) arrives, she is very impressed with Tidy's clean algae bed, and appreciates the kelp forest.

While camping, Splash and Bubbles admire all of the beautiful sparkles in the sky. The kids soon think that those sparkles may have fallen from the sky into the sea when they see a brand new light show in Reeftown. / Splash, Bubbles, Dunk and Ripple play a big game of hide and seek with Tyke, the Pacific harbor seal in the Kelp Forest. When they temporarily can't find Tyke, they are relieved to learn that even though she's quite independent and curious, she won't wander far from her home.

After visiting a spooky cave, Splash and his friends visit the spookiest place they know, the cave of the old hagfish, who lives deep in the abyss. / Dunk gets spooked by a creature in his home and thinks it's a monster, only to discover a Baby Sea Urchin who is hiding from a giant "Thing" that circles in the waters above the reef - Mayor Sting!

Mayor Sting has to attend a stingray migration, which will take him away from the reef. Dunk volunteers to fill in as the mayor for the day, thinking it will be an easy job, but has no idea what it takes to keep the reef thriving and safe. / When Bubbles goes looking for the ultimate mud puddle, she ventures down to the Deep, where Lu takes them to see a hydrothermal vent and meet some lipstick tubeworms and Oblo the blobfish.

When Splash and Bubbles hear that one of Ripple's Brothers has wandered off, they join Ripple's search, while enlisting the help of Zee and her new friend, Hamilton the hammerhead shark, to find him. / Maury discovers Denny's molted exoskeleton in the reef and assumes something must be wrong with "the real Denny," so he enlists the help of Splash and friends to find her, only to discover that she has simply molted.

Splash and Bubbles stop to visit Tidy for the day, but find him exhausted from constantly cleaning up behind the new kelp forest resident, Tyke, a young female Pacific harbor seal pup. Splash and Bubbles try to help Tidy by seal-sitting the young seal pup, and quickly learn how hard it is to keep track of their curious and fearless new mammal friend. / Splash and Bubbles realize that Zee is alone on the reef as the only shark, but when they learn that she has a distant relative in Reeftown, Zee is excited to discover who it is.

Chompy the Parrotfish decides she doesn't want to eat only algae anymore when she sees Splash and his friends eating a variety of things found in the water column (plankton, etc.) The others have to get Chompy back on her normal eating plan before the reef gets overrun with algae! / Bubbles and Ripple meet a jellyfish. However, when they bring Splash and Dunk to meet her, they discover she doesn't remember them at all. The kids learn that what they thought was one jellyfish were actually two identical clones of each other.

When Lu's light goes out, Lu has trouble attracting food and seeing down in the Deep, so the kids decide to show her a world filled with light - the reef. There they realize that Lu's light didn't go out, it's just covered with mud. / On a sleepover with Zee, Bubbles is fascinated to learn that Zee is nocturnal. Zee can't help it, she goes out to play and look for food at night! Bubbles is so excited about this new discovery that she tries to stay up with Zee to learn about and explore what it's like to be nocturnal.

When Splash and his friends are playing at the sandy bed, they find a parrotfish munching on some coral and helping to create the sandy bed on which they're playing, because parrotfish produce sand from their bodies after they eat. / When Bubbles gets trapped in a treasure chest, Splash and his friends can't get her out. Luckily she's not alone when they discover Wave in there, who they think is also stuck until he show that being an invertebrate means he can squeeze even tiny spaces.

After visiting a spooky cave, Splash and his friends visit the spookiest place they know, the cave of the old hagfish, who lives deep in the abyss. / Dunk gets spooked by a creature in his home and thinks it's a monster, only to discover a Baby Sea Urchin who is hiding from a giant "Thing" that circles in the waters above the reef - Mayor Sting!

The Reeftown Rangers wonder where the end of the ocean is, or if the ocean even has an end. They venture out to find the end of the ocean and discover a rainbow salmon, Sal, who teaches them about the difference between fresh water and seawater, and about where all the water goes beyond the ocean. / Splash, Bubbles, Dunk and Ripple travel to the Antarctic and meet a new friend, Dive, a gentoo penguin who can live in and out of the water. Dive wants to be a Reeftown Ranger, but needs to learn that he is not just like a fish!

Splash takes his pals to go see his friend, LU, a fearless explorer in the deep. He has met Lu in his travels, and she has been an inspiration for Splash. Lu turns out to be a female football fish (the "Lu" stands for "bio-LU-minescent") who leads them on an adventure in the abyss. / Wave, the octopus, loves the musicality of Reeftown, but tries to keep others from discovering that he has no rhythm.

The Reeftown Rangers discover that, unlike them, Melody the fin whale migrates twice a year to follow the krill. Inspired by Melody, Splash and the others attempt to experience migration for themselves, beginning in the Antarctic, where they meet Mac, a mackerel icefish. / The Reeftown Rangers, continuing their migration adventure in the Antarctic, meet Pebbles, a gentoo penguin, and learn that she will receive a gift of a pebble from a male penguin who wants her to be his partner for life.

The Reeftown friends arrive at the Arctic, where they don't find Melody, but instead meet Whistler, a narwhal who is a very unique creature with many interesting attributes, including a tusk on his head. / The kids finally find Melody just in time to see her at the krill bloom, where they learn all about the food chain going from the tiny krill all the way up to the huge whale. Their journey ends by hearing the beautiful music of the humpback whale before returning home to Reeftown.

Splash sees a beautiful fish go by and instantly wants to be its friend, but whenever he tries to talk to the fish, it ignores him. He and his friends soon learn the fish has false eyespots on her back and had no idea they were trying to talk to her. / When Finny, a green dragonet, joins the group to play one day, Bubbles starts to worry that they're so similar, her friends won't need her around anymore.

Gush travels with the kids to the Arctic Ocean to finally find the mysterious "horned whale," which has eluded him for a long time. As it turns out, what they see is not really a "horned whale," but a narwhal. / After hearing that a great white shark has a toothache, Splash and friends enlist Denny to help, not realizing that in the world of cleaner shrimp cleaning the teeth of the great white shark is a revered accomplishment.

After visiting a spooky cave, Splash and his friends visit the spookiest place they know, the cave of the old hagfish, who lives deep in the abyss. / Dunk gets spooked by a creature in his home and thinks it's a monster, only to discover a Baby Sea Urchin who is hiding from a giant "Thing" that circles in the waters above the reef - Mayor Sting!