Cap'n Turbot and his cousin Francois go deep sea diving to snap a picture of a rare seaslug - the only problem is their diving bell ends up stuck, and then the propeller fin breaks at the bottom of the bay! It's PAW Patrol to the rescue, and they have just the right vehicle - Zuma's new submarine!
The episode starts with the pups playing volleyball, when Skye notices the baby whale wanting to join them. She says the baby whale can play with them later, and the baby whale leaves with a whimper.
Meanwhile, Cap'n Turbot and Francois are preparing to go underwater in a diving bell to get a picture of the rare giant sea slug. As they descend, the baby whale, thinking the diving bell is a volleyball, decides to play with it. While Cap'n Turbot enjoys the baby whale's playfulness, Francois doesn't. However, because of him enjoying the baby whale's playing with the diving bell, Cap'n Turbot forgets to restart the engines afterwards, and the diving bell plummets to the seabed, severing the steering fin when it collides with a rock outcropping, and leaving the bell to get jammed between to large rocks. Trapped, Francois starts to panic, but Cap'n Turbot knows just who to call.
Ryder is out on patrol on the mountain road when he gets Cap'n Turbot's call for help. Pulling over on a roadside curb to answer it, Ryder learns of the plight that Cap'n Turbot and Francois are in. Assuring the pups are on their way, Ryder calls the pups a little differently from normal since the pup-pad was locked into his ATV's steering wheel: He accesses the pups' summon button similar to when he shuffles through to contact them or select who he needs for a mission.
The pups report to the Lookout, but Marshall, who got tangled in the volleyball net, ends up bringing along an unexpected extra passenger: A resident who had been on the beach reading her book when Marshall unintentionally snagged the hook of the volleyball net on the front of her chair. Apologizing once she takes notice, Marshall then pushes the chair back out of the elevator, telling the resident to enjoy her book, and the team head topside. When Ryder reveals that Cap'n Turbot and Francois are in trouble, the pups are very worried, Skye especially for Francois. With them needing to dive deeper than usual to reach the diving bell, Ryder assigns Zuma to assist with his submarine, much to Zuma's excitement, and Rocky for the repairs. Rocky hopes that they will bring the diving bell up so he won't have to get wet, but it's clear that he might still have to if they are unable to bring it to the surface. The team deploys, and once they get to where Rocky will wait for them on the beach, Zuma has his hovercraft convert into it's submarine mode, allowing Ryder to join Zuma as he heads down to help Cap'n Turbot and Francois. Rocky stays behind to enjoy getting some sleep and sun on the beach.
Once Zuma and Ryder reach the diving bell, Zuma uses his sub's rescue arm to pull the diving bell free. Once free, Cap'n Turbot tries to steer it without the steering fin, but only sends himself and Francois for a spin, where impact with the seabed causes a couple of rivets to pop out and cause water to start to fill the inside of the diving bell. Cap'n Turbot attempts to try and surface the bell, but only drives it out of control again, colliding with Zuma's sub, and sending it to land upside down next to where the severed steering fin landed. Ryder contacts Cap'n Turbot to power down the bell's engines. Once that's done, Zuma rights his own submarine, before Ryder calls Rocky and tells him it's time to dive.
A little later, Rocky is loaded up with his own scuba gear alongside Ryder and Zuma, and after some hesitation, heads down to help with repairs. Back at the bell, Francois starts to panic, and when Cap'n Turbot says to wait, Francois refuses, and attempts to drive the bell to the surface while it's still uncontrollable. However, once seeing Ryder and the pups approaching, Francois completely forgets about his little mutiny, and only annoys his cousin by saying that it was a good thing they waited for Ryder, when it was clear Francois just said he wasn't going to wait himself.
With Rocky's help, the steering fin is repaired, and the Cap'n and Francois can return to the surface. Before they can however, the sea slug they had been looking for appears right next to them, giving them the perfect chance for both Turbots to each get a picture of it.
Back on the surface, Rocky wonders when the diving bell will surface. To answer his question, the bell is brought up by the baby whale, once again thinking it's a volleyball. Annoyed by the baby whale's alternate means to not being able to play with the pups, Rocky finally decides to give the baby whale what it originally wanted, overcomes his aquaphobia for the moment, and swims over to allow the baby whale to have some fun with him. Rocky actually enjoys the fun he's having with the baby whale before it sends him like a skipping stone safely back onto the beach, much to his gratitude.
Later, Ryder has set up the volleyball net again so the pups can play again, while as for the resident that Marshall brought with him to the Lookout by accident, she plays it safe and pushes her chair as far away from the pups as she can to avoid a repetition of earlier. Cap'n Turbot and Francois soon show up to offer their thanks, and show Ryder their pictures of the sea slug. Unfortunately, Francois' picture is ruined as his thumb got in the picture and obscured most of the slug from view. Cap'n Turbot's turned out better as he got a great picture of the slug. Afterwards, the Turbots join Ryder and the pups with playing some volleyball. In the end, Cap'n Turbot and Marshall go for the ball at the same time, and both end up tangled in the volleyball net. The episode ends as Francois, Ryder, and the other pups all laugh as Cap'n Turbot jokes that he now knows what a beached burrito feels like as he and Marshall remain tangled in the volleyball net.