After an encounter with a school of migrating tuna, the Octonauts discover that one of the speedy fish, Tina, has been left behind. And she’s injured! Poor Tina has a hook stuck in her mouth and is too weak to swim. After Peso tends to her wound, the Octonauts agree to help get her to the tuna spawning grounds. But they’ll have to be quick: egg-laying season doesn’t last long. Luckily, Tweak’s latest gup, the Gup-R, is the fastest she’s ever built! The Octonauts use it to tow Tina, but when the Gup-R’s battery dies, how will they catch up to the rest of her school?

When Kwazii discovers a blue whale with an injured tail, the Octonauts attempt to use a giant net and Octofloats to keep it from sinking. Meanwhile, Peso and Tweak collaborate on a special brace for its tail, and Kwazii, Dashi and Shellington try to find it enough food. But when the supporting net breaks, the Octonauts have to launch an emergency free-fall rescue!

Shellington is excited to find the distinctive tooth of a very rare creature, the spade-toothed beaked whale. Now, the Octonauts must find the tooth’s owner, so Shellington can study it, and so that Peso can help replace its tooth. But it won’t be easy: spade-toothed beaked whales like to be left alone and can dive very deep.

The Octonauts follow a trail of deep-sea debris to its source: a derelict ship floating unmanned on the surface. But the ship seems to be haunted by ghostly voices, which a quick dip below the water line reveals to be hundreds of barnacles stuck to the ship. As the ship drifts into waters too cold for the barnacles, the Octonauts must find a way to tow it to warmer waters before it sinks or falls apart.

While exploring a reef, Shellington and Dashi accidentally trigger a feeding frenzy with multiple sharks biting at anything that moves. As Barnacles and Tweak work frantically to plan a rescue, Shellington and Dashi try not to become shark food!

Kwazii sets off on a monster hunt, and soon encounters a shelled creature called a Nautilus.

The Octonauts must help reunite a grey whale calf with his mother, keeping him well fed in the meantime.

The Octonauts meet a flying squid who can help Kwazii's grandfather, Calico Jack, retrieve his treasure.

When a wave traps Dashi in a cave with an injured sea lion, the Octonauts and sea lion pack must work together to save them. Using just some rope and a life buoy the pack fights against the waves to save them. Can they save them before it is too late?

The Octonauts must guide an ill-stricken hawksbill sea turtle into cooler waters, in order for her to lay healthy eggs.

When Kwazii is found with an injury, he tells the tale of how he and Calico Jack encountered a fish that ate his peg leg.

The Octonauts help a band of algae-shooting sea squirts reunite in order to stop an outbreak in the reef.

When the Vegimals accidentally bring bullfrogs into the Octopod, they must rally them up and bring them back home before the Octonauts find out.

Kwazii and Shellington get lost in the Antarctic’s deep seas, before meeting a family of giant sea spiders who may know a way out.

When the Octo-Bots sink into a lake of boiling hot sulfur, Kwazii has to rescue them before the surface hardens.

Captain Barnacles and Kwazii help a pair of singing female axolotls named George's mom (yellow) and George (pink) find a new watering hole, while protecting them from a hungry flock of herons.

In order for a school of salmon to reach their nesting area, the Octonauts must enlist help from a family of beavers.

The Octolab is being eaten away by a group of zombie worms, tasking the crew with finding a new home for them.

While exploring the Mariana Trench, Shellington and Dashi come across a path full of mud volcanoes and a creature in need.

The Octonauts encounter a tiger fish and blind shrimp who become separated.

The Octonauts help a creature find his louse friend who got lost and could be in trouble.

Shellington’s sister and nephew, Pearl and Periwinkle, join him on a mission.

The Octonauts encounter a blob of glowing liquid drifting on the ocean’s surface.

The crew must catch a mysterious fish that’s out to bite every creature in the reef.

The Octonauts meet strong scaly foot snails and enlist them in trying to help save the Octo-Lab from falling into a crevice.

The Octonauts head to the Yangtze River to help Min the Mapmaker, an old friend of Inkling's, who's been trapped by a mysterious creature. Turns out, It was just a Chinese giant salamander protecting her precious eggs, which have fallen ill due to rising water temperatures.