When Kwazii's favorite sub, the Gup B, goes missing, the Octonauts journey into a mysterious kelp forest to find it, meeting strange and interesting creatures along the way.
The Octonauts land on an island for a picnic but must first help some crabs trapped between two warring groups of aggregate anemones. Meanwhile back on the Octopod, a horde of out of control puddings are attacking. Peso wins the contest between 2 types of blobs.
While exploring the Arctic, the Octopod gets trapped in the ice. Only Barnacles's skillful navigation, and the help of a friendly Narwhal, can get them free.
While exploring the deepest part of the ocean, the Midnight Zone, the Octonauts discover a strange rock that happens to be home to a new species of worm.
The Octonauts race against time to rescue Tweak's pal, a leatherback sea turtle who's caught in a fast-moving ocean current that's sucking it into a whirlpool.
When Peso's little brother, Pinto, comes to visit, he's more interested in being a pirate than a medic – at least until he accompanies Peso on a mission to rescue Dashi and Shellington in a kelp forest.
When important objects go missing from their ship, the Octonauts stake out the thief, who turns out to be a decorator crab stealing their things to decorate his shell.
The Octonauts lead a pod of Beluga Whales stuck under the pack ice to safety by getting them to follow Peso while he's playing the same tune as the Beluga's song on his xylophone.
The Octonauts are chased by a whitetip shark only to discover all it really needed was a pilot fish to clean its teeth, and it just so happens that they have just met a lonely pilot fish that is hungry for action.
Peso must gather all his courage when he travels deep down to the very bottom of the ocean, the Midnight Zone, and encounters the mysterious Vampire Squid.
After a storm, the Octonauts help a female seahorse search for her missing mate. She tells them, to Kwazii's surprise, that the missing male seahorse is about to give birth to baby seahorses!
Some mysterious holes that keep appearing in the Octonauts' equipment turn out to be the work of cookiecutter sharks whose bioluminescence initially made them invisible against the light coming down from the sea surface.
When Kwazii and Peso are shipwrecked on a desert island, they encounter a Combtooth Blenny - a fish who walks on land! They enlist him to send an SOS message to the other Octonauts.
Some electric torpedo rays give the Octopod a jump-start when its batteries go flat during a trip to see Tweak's pal, Sandy the leatherback sea turtle.
The octonauts help a 100 year old spider crab which has got its leg trapped in a giant clam whilst en route to its own 100th birthday party. It turns out that Kwazii's afraid of spiders, but he still helps, even though he thought it was a real spider at first.