When no clues are found, Bunga suggests fighting Scar head on, but Kion notices some suspicious paintings, that is cut off by a large boulder. After a lot of pushing, Beshte is able to move the rock away, revealing another passageway and the rest of the paintings, including one with the Mark of Evil. Makini brings the painting to life and explains how it seems to suggest that Askari's Lion Guard once fought a great evil, and how the secret to defeating that evil lies in a chamber, deep within the lair. Makini stops them from entering at first, showing them a painting which warns them of the dangers within. The Lion Guard is confident in their abilities and enters regardless, with Kion suggesting that Makini stays behind for her safety.
As the Lion Guard proceeds they discover another painting on the wall. Bunga tries to decode it in Makini's absence but fails. Beshte agrees with Kion that bringing Makini down could be dangerous when suddenly the ground beneath his feet breaks. The cracks spread over to Kion, Fuli, and Bunga, and all but Ono fall onto a rock slide. Ono notices some sharp rocks ahead, and Beshte skids to a halt, grounding himself. The rest of the Guard bump into Beshte, safe from harm. Fuli questions how they will return to land, but Kion notices another pathway. Reminding them that the chamber is deep, the Lion Guard follow it down.
When they arrive at the bottom, Fuli discovers another painting. Knowing that they are on the right path, the Guard continues forward, until they come to a crossroad. Bunga assures them, that he has experience with caves and leads them down a route, only to wind up at a dead end. Bunga is certain that it's another secret passage and attempts to open it, but eventually gives in and concludes that it really is just a wall.
Meanwhile, Makini watches the tale of how Askari led some animals to Mizimu Grove. She moves across to view more paintings but notices how far she is from the entrance. Remembering that the first painting warned her that it was dangerous there, she turns back but soon halts when she remembers that all the paintings would have been painted by a Royal Mjuzi like herself. She decides to view a couple more paintings.
The Guard continue their efforts to move forward but wind up encountering dead ends at every turn. Bunga tries once more to open a secret passage, but fails, leading Fuli and Kion to confusion. Noticing a tall rock, Kion asks Ono to take a look at what they're dealing with. Ono reveals that the entire area is a maze, much like in the painting they saw outside. He locates the path they're looking for and guides them out.
Elsewhere, Makini continues her examination of the paintings, when she notices the painting which Kion's Lion Guard first saw when they entered the new cavern. While looking, the pathway beneath her crumbles, and, after making the painting come to life, fears for the Lion Guard's safety. Without wasting another second, she leaps down the slide.
Ahead of her, Ono guides the rest of the Guard into a new area. They discuss how lucky they were to have both the strongest and keenest of sight with them until Kion realizes that the whole thing was a test to see if they were worthy of finding the secret. Bunga comments that only they would be able to progress that far, when Makini arrives, having followed their footprints in the maze. Kion is still a bit wary of allowing her to join them, but he's reminded that a Royal Mjuzi had to have been there to paint their adventures. Kion agrees to let her accompany them but also reminds everyone to be on the lookout for the next test.
They move through a passage and enter a chamber with a large canyon below, and an entrance at the other side. The gap between the paths is too big for anyone to jump. Bunga suggests that Ono is being tested again, this time for his flight until he's reminded that all previous Lion Guards were strictly lions. Makini calls them over, having found another painting, this time of the bravest lion. When she brings it to life, it shows him walking over the crevasse, seemingly on thin air.
Bunga decides to leap over the crevasse, much to the horror of his friends. But instead of falling down when his jump wasn't enough, he instead lands on what appears to be thin air. It doesn't take long for Ono to work out that there is, in fact, a bridge over to the other side, and that it's an optical illusion. The Guard cross over and Makini excitedly informs them that she'll paint the invisible bridge when they return. Fuli questions her on how she'll paint an invisible bridge, and Makini realizes that she can't.
In the next area, Makini notices another painting which suggests that they're close to the final chamber. However, a large boulder blocks their path. Beshte considers moving it but realizes that he's already had his test, prompting Bunga to reach the conclusion that maybe it's just a rock. After he knocks on the boulder, it comes loose, and everyone starts to run. Kion asks Ono to check for an escape route, but the passage is too narrow. Fuli then has an idea. She stops and leaps onto the top of the boulder, reaching her claws in and running across it in order to slow it down. When this fails, she switches around and starts to speed up the boulder, pushing it along the walls in order for it to go around everyone. Everyone commends Fuli for her quick thinking, and they continue on their journey.
Bunga ponders on what Kion's test could be, but in doing so, he accidentally walks into a rock that sets off a small avalanche. With everyone trapped in total darkness, Kion begins to roar softly in order to get a feel for his surroundings. With the others stumbling over one another, Kion asks them to follow his voice, while he uses his roar to determine empty areas and locate a pathway out using his echo.
The group finally locate the exit and are in awe at the final chamber, which is decorated with small pillars containing more paintings. They are soon called over by Makini, who locates the story of what happened all those years ago.
According to the paintings, many years ago, a group of evil lions tried to take over the Pride Lands. In doing so, they nearly destroyed it. Thus, the good lions of the Pride Lands created an unstoppable force to defeat the evil lions, but only the worthiest in the Pride Lands would be able to find and use the force. When Kion questions where the force is, Makini spots another painting, it directs him to another room nearby. Kion and Makini lead everyone into the room.
In the room is a pool of water and another cave painting. Looking to discover the source, Bunga leaps into the water but is unable to find any secrets in it. But Kion realizes what the force really is after seeing his reflection - it's them. Makini brings the last painting to life to confirm Kion's theory, showing how Askari's original Lion Guard was formed to stop the evil lions.
Makini apologizes, with her belief that she could have noticed the signs earlier and thus saved the Guard the hassle of going through the tests in the first place. But Kion states how much they needed to go through them so that they knew they were worthy. Filled with new invigoration, the Lion Guard peers up at the Mark of the Guard painting on the wall and cry out their battle cry, ready to take on Scar.