When Makini chases some mysterious blue lights, she and Ono get trapped in a cave.
The Lion Guard is seen walking through a marsh, with Kion urging the group to go on, wanting to get out before nightfall. Frustrated by the damp marsh, Fuli questions if they really have to go through it, though Kion assures her that they'll be on the other side soon. Anga agrees with Kion, spotting the next Moja Kwa Moja Stone just beyond the edge of the marsh. Bunga tries to convince Fuli that the marsh isn't so bad, saying the snails are great. Fuli points out that it's only nice for Bunga since he's not in the mud, However, Bunga says that he loves mud before jumping in, covering Fuli with it.
Shaking off the mud, Fuli angrily wonders if things could get any worse just as they hear a group of screaming animals running towards them. After Ono and Anga fail to identify the animals, Makini grabs Ono in a panic and runs off, wanting to protect him despite his objections. The rest of the Guard stays behind to confront the animals, who turn out to be a pack of mongooses that attack them. Though Kion tries to reason with them, the mongooses refuse to listen, only wanting to fight. Still, despite their numbers, the mongooses fail to harm the Guard, acting like annoying pests more than anything.
Far away from the fight, Ono gets Makini to stop after realizing they can no longer hear the Guard. On their way back, however, Makini spots a floating blue light ahead, which Ono states are a marsh light. Distracted by their beauty, Makini drags Ono around with her as she follows the lights all over the marsh, ignoring Ono's warnings that they will get lost. After the lights disappear in a clearing, Ono starts to feel nauseous. Makini apologizes to Ono for not listening to him. Now lost and having to act as eyes for the both of them, Makini cluelessly begins her way through the marsh just as the floor gives beneath them.
Meanwhile, the mongooses have started throwing mud at the Guard. After failing to reason with them, Anga picks up the mongooses before scattering them away. Not knowing what angered the mongooses, Kion starts asking Ono before finding both him and Makini missing, causing Beshte to remember their departure. At that point, Ono and Makini are in a cavern below the marsh. After failing to climb out of the cavern, Makini suggests that Ono fly out and get help, though Ono shoots down the idea on account of his eyesight. This leaves them both trying to come up with an idea to get out.
Above ground, Anga fails to spot Makini and Ono due to the trees. After catching onto their scent, Fuli begins leading the guard through the marsh. Bunga, meanwhile, starts competing with Anga over who spots Makini and Ono first, the prize being a snail. At that point, however, the mongooses make a comeback. No longer in the mood to deal with them, Kion decides to make a break for it, hoping to find Makini and Ono in order to leave the marsh and find the next moja kwa moja stone. Relieved, Fuli leads the guard away from the mongooses, who swear to return as their fight isn't over yet.
Back at the cavern, Ono is unable to think of an escape plan as Makini loudly attempts (and succeeds) to grab an overhanging tree root. However, the tree root breaks under Makini's weight, causing water to start pouring into the cavern. Now desperate, Ono orders Makini to sit still and to not do anything, though Makini soon breaks through a wall after leaning on it, finding a tunnel behind it. Not having many options, Ono and Makini go through the tunnel to escape the rising water. Soon after, a colony of bats flies through them, much to Ono's horror (since he is afraid of bats). However, Ono then realizes they can follow the bats out of the cave.
However, they soon come across two tunnels without knowing which one to take. Remembering that bats travel through by listening to the echoes of their chitters - echolocation - Ono suggests that they travel the same way. However, Makini's loud nature annoys Ono, who needs silence in order to listen to the echo. Above ground, the Guard is still looking for Makini and Ono. Though Anga discovers Makini's tracks, Bunga takes credit for the deed and declares himself the winner, prompting Anga to drop him in the mud. The Guard then realize that Makini had run around in circles, scattering her scent all over the place.
Back in the tunnels, Ono tries snapping his beak to hear the echo, though Makini's talking annoys him and makes the task impossible. Almost fed up with the mandrill, Ono slowly and firmly reminds Makini to be completely silent and listen. Ono tries snapping his beak again, though Makini notes she doesn't hear the echo. Frustrated, Ono realizes the plan isn't working because bats make louder and higher-pitched noises than the ones he makes. Makini starts suggesting that they make a loud and high-pitched sound themselves, causing Ono to realize that they can use Makini's own voice to create an echo.
Excited, Ono tells Makini to shout anything at the tunnels, causing her to literally shout "anything" to guide their way through the cavern. Now in sync, they realize they make a great team when Ono notices they're getting close to the surface. Above ground, the Lion Guard is shown looking around for clues to find Makini and Ono. Bunga soon finds the hole to the cavern, though he ignores it to look for snails, finding them under a rock. Soon after, the mongooses start screaming again as they lead a charge against Bunga. However, Kion quickly steps in and pins the leader, Krud'dha, underneath his paw.
Having had enough, Kion asks why the mongooses keep attacking them, with Krud'dha explaining that Bunga keeps eating their snails. Stopping the mongooses from attacking Bunga, Kion tries apologizing for their mistake, though Krud'dha shouts that they want their snails and the Guard out of the marsh. Kion says that they won't leave until their friends are found. Soon after, Makini dramatically emerges from the ground, scaring the mongooses. After pulling Ono from the ground, Makini falls back over a log that breaks, covering the ground with snails. As the mongooses rush over to feast on the snails Fuli holds back Bunga from joining the feeding frenzy.
Standing up, Ono recognizes the mongooses, pointing out how much they love eating snails. Ono and Makini begin explaining their story, before agreeing that Makini kept him safe and that they make a great team. That night, Anga is shown leading the Lion Guard to the next moja kwa moja stone, which is just up ahead. On the way, however, Bunga spots a marsh light and runs after it, though Anga grabs him before he gets lost. Enjoying the view from above, Bunga spots more snails and asks Anga to let him go. Anga refuses, returning to the Lion Guard as they make their way out of the marsh.