Mayor Goodway, Farmer Yumi, and Chickaletta are going diving in the coral reefs just offshore of Adventure Beach while the Turbot cousins are having lunch on the Flounder. As they enjoy their scrumptious lunch, they notice several sea creatures acting strangely. Seismic activity soon followed along. Curious and concerned, Cap'n Turbot checks his radar and discovers that a volcano is forming underwater. After some small arguments where the Turbots realize they are saying the same thing coincidentally, they proceed underwater in the diving bell to check it out.
Back on Adventure Beach, Farmer Al arrives with blueberries for the pups to eat. Marshall activates his pup-pack's water cannons and starts washing them clean, only to be interrupted by the rumbling of the volcano, causing him to splash Rocky by mistake. Concerned about the rumbling, Ryder returns to the Beach Tower HQ. He is soon contacted by the Turbots, warning him about the volcano. Knowing that the eruption will cause a lot of ash and rough waters, Ryder decides to close Adventure Beach for safety reasons, and after telling the Turbots to evacuate the area, he contacts Mayor Goodway on her cellphone, but gets Al instead. Learning that his wife and Mayor Goodway are in danger, Al is deeply worried, but Ryder re-assures him that they will get them to safety. He then summons the pups to the Beach Tower HQ.
As the pups run, Marshall trips over some pup-bowls and spills the blueberries all over the pups while trying to enter the Beach Tower HQ. He cracks a "feeling blue" joke and they all trade laughs before going in. Once inside, Ryder briefs the pups of the situation, and assigns Marshall to find the divers. He also assigns Chase to clear Adventure Beach and the water of civilians. The Sea Patroller is then loaded up with Marshall and Chase's boats, and they all take to the sea.
Once they reach the area where the volcano is, Chase is deployed to evacuate Adventure Beach, and Marshall is deployed to locate the diving flag marking where Yumi and Goodway went under. Once he finds them, he warns them of the danger but soon discovers that Chickaletta wandered off. Marshall goes after her swiftly, assuring Mayor Goodway he'll find Chickaletta. He also warns them that they needed to get out quickly, and that the Sea Patroller would pick them up once back at the surface.
Back with the Turbots, another argument causes them to get the diving bell jammed in the mouth of the volcano's crater as it is about to erupt. Cap'n Turbot calls Ryder to warn him of the situation, and Ryder takes Zuma and deploys in the Sub Patroller to rescue them. Upon reaching, Ryder asks Zuma to activate the Sub Patroller's grabber arms to pull the Turbots' diving bell out of the crater. With some effort, they manage to pull the diving bell loose, but as the Turbots prepare to escape, the volcano sends the diving bell up for a spin before clunking it back into the crater where it gets stuck again. At the same time, Marshall finds Chickaletta who was following a sea cucumber thinking it was a pickle, but a smaller thermal vent from the volcano shoots them up, causing them to land on top of the diving bell. Without any warning, the volcano blows the diving bell, together with Marshall and Chickaletta, out of the water, sending it airborne. No longer underwater, Marshall de-activates his scuba mask and holds on to Chickaletta to ensure her safety. As the effects of gravity began to act on the diving bell, Ryder sends out Skye in her seaplane to pass Marshall a parachute to slow the diving bell's decent. De-activating the rest of his scuba helmet, Marshall affixes the parachute's hook to the diving bell's handle, and the parachute slows the diving bell's decent, allowing it to land safely on the Sea Patroller after Ryder has Robo-Dog navigate it into position to catch it.
As everyone re-groups and heave a sigh of relief, the continuous rumbling from the volcano attracts their attention and they realize that the volcano has breached the surface and formed a new island. Upon their amazement, Francois and Cap'n Turbot get into another argument about what to name the new island and everyone shares a laugh over it.