Kion unleashes his Roar again when Simba and Rafiki approach them. Rafiki states that the Roar is getting stronger as Kion gets older. Simba agrees, and announces that it's time to defeat Scar once and for all. With Jasiri offering to help as well, they come up with a plan and gather the Pride Landers to strike the Outlands that night. However, some skinks overhear their plan, and slither away.
Meanwhile, at the destroyed Kilio Valley, Janja sits on a rock, talking to Cheezi and Chungu about how Kion's Roar is now more powerful than ever. Janja expresses his annoyance at constantly being defeated and begins to wonder if they might be on the wrong side, wondering if Jasiri was right all along and that there could be A New Way to Go. When his friends ask what he's speaking about, Janja shrugs their concerns off. However, two more skinks overheard him questioning his loyalty to Scar.
In the Outlands Volcano, Ushari is speaking with Scar, having received news of Janja's possible reformation and the impending attack from the Pride Lands. Scar is undeterred, and it isn't long before Shupavu's Group comes to Scar with Janja in tow, as Scar had requested. When Janja walks in Scar orders him to go the Lair of the Lion Guard and not let the Guard out. He explains that he wants the hyenas to distract them, and voices his concerns to Janja that Kion could destroy him if he uses the most powerful Roar he can muster in the caldera, hence why he needs to strike back. Janja obeys and leaves, with Shupavu's group following him after being ordered to fetch Reirei's Pack, Kiburi's Float and Mzingo's Parliament. Scar assures Ushari that he's always two steps ahead.
Later that night, Zazu alerts the royal family that Hadithi has just arrived with their ally, Shujaa have come to help. With all the Pride Landers gathered together, Simba asks Kion to lead the battle in the morning. Kion confesses that he has concerns over how to defeat Scar, but Simba remains positive. Soon, Kion and the Guard start to think to talk of the building anticipation that this is the last night before the big battle, with Kion needing to speak with someone beforehand.
Meanwhile, Kion speaks to his grandfather Mufasa. He is worried that there's no way to defeat Scar. Mufasa is as confident as Simba that Kion can handle it, and reminds him to be himself, and not to fight fire with fire.
Back near Pride Rock, Janja's clan enters the Lair of the Lion Guard so they can trap the Guard, grabbing Ono's attention. When the Guard enter, Reirei and Kiburi add more dry grass and sticks to the entrance, and before long, Mzingo's parliament set them alight. It doesn't take long before the lair fills up with smoke. Janja escapes the fire and, realizing Scar has betrayed him, goes to find Jasiri, the only one who will trust him.
Ono flies out of the lair to discover the entirety of Pride Rock is on fire, and Kion orders him to save his family. With help from Anga and Hadithi, the royal family is lifted to safety.
With time of the essence, Beshte remembers that the lake in the pool leads to Lake Shangaza just outside the lair. When Janja's clan ask to follow, Kion allows them to do so, telling them that he respects all creatures, even those who don't follow the Circle of Life. With Fuli grabbing onto Beshte, the Guard and Janja's clan swim through and out the other end, where they notice the severity of the fire.
With the royal family safe outside Pride Rock, Scar appears on top of the burning Pride Rock and announces that the Lion Guard weren't so lucky to escape. But he and the Guard shows up with Janja's hyenas next to their side, but Scar says that there's no way to defeat him before vanishing. The herds begin to panic, when Jasiri and Janja arrive. Janja offers advice on how to defeat Scar based on what he heard earlier from him, which Kion takes. They set up the plan and get some rest.
Back in the Outlands Volcano, Scar tells Ushari of how he lied to Janja and that Kion's Roar can't defeat him. He then proceeds to tell Ushari the story of how he got his scar when he led his Lion Guard. A lion fooled him, leading him to a cobra that attacked and gave him his scar. The strange lion promised to cure the venom provided he did everything he ordered. Enraged, Scar used his Roar and destroyed them instead. When he returned to Mufasa, the King merely nicknamed him Scar, causing him to resent his brother. This was what triggered Scar to destroy his Lion Guard, lose the Roar, kill his brother and take over Pride Rock before Simba defeated him. He tells Ushari that the next part of the plan will involve him, and explains his plan.
The next morning, Kion leads the assault on Scar's army. They fight against Reirei's pack, Kiburi's float and Mzingo's parliament, slowing them down Kion and the Guard aim for the volcano. Scar orders Shupavu's group to slow them down, all to give the impression that they don't want the Guard to reach him.
The Lion Guard soon enter the volcano, and make their way to Scar. Scar orders Ushari to charge at Kion, resulting in a scar of the cub's own. He proceeds with Jasiri's signature catchphrase: 'Sisi ni Sawa', to remind Kion how alike they are, but Kion refutes his remark by offering Scar his forgiveness. He tells Scar that he cannot judge him for his previous actions in everything, and that only the Lions of the Past can do it. He takes a deep breath and blows softly to the air, prompting the Great Lions to appear in the sky. They send down rain from the heavens that melts Scar away, but not before he warns Kion that the Roar is a curse. Desperate, Ushari tries to avenge Scar by attacking Kion, but Bunga tackles him into the lava. Ono grabs Bunga from falling to his death, but Ushari meets his fiery fate.
Kion and the Lion Guard emerge out and the Pride Landers cheer. The Outlanders are shocked that they no longer have a leader, but Janja takes the initiative to say that Jasiri should be in charge. Jasiri announces that she is certain they can all get along if they all respect the Circle of Life, and Janja announces that he will be helping her keep everyone in check, by joining her clan. Knowing that Jasiri will take care of Janja, Reirei gladly accepts. Kiburi is adamant that crocodiles can fend for themselves. Mzingo declares that a vote would be more suitable, but the hyenas chase him away. Nearby, Ono is unable to see what's going on, and the Lion Guard decide to return to Rafiki for help. With everything settled in the Outlands, Kion thanks Jasiri once again before leaving.
On the way back, Kion falters as his scar begins to hurt. Bunga returns to his friend, only to be roared at. He is distraught that his roar slipped out at his best friend, so his friends suggest that he see Rafiki for some help. Ono also hopes for help with his eyes.
They return to the mandrill, who says that there's nothing he can do about Ono's eyes, which has become damaged due to the vog from the volcano, and that only time will tell if it will heal. However, for Kion's scar, while the scar itself cannot heal, he will need a cure for Ushari's venom. To this end, he suggests a visit to the Tree of Life, since all he can offer him is Tuliza, a temporary relief for Ushari's mind altering venom. Ono wonders if the Tree of Life could help him, too. The Lion Guard agree to travel with Kion, but when the subject of the Keenest of Sight comes into play, Ono suggests that Anga replaces him. She is hesitant, but Kion declares her the new Keenest of Sight after a bit of encouragement from Ono. But he still wishes to have Ono on the Guard, but as the Smartest.
Now with six members on the Guard, the Guard get ready to leave the Pride Lands. Simba and Nala wish them good luck and hope he can return before Kiara's first hunt. Makini also joins the Guard, keeping a good stock of Tuliza in the Gourds on her Bakora Staff. The Lion Guard leave with Pride Landers wishing them goodbye. Kion stops to talk with Thurston who says that the zebras will protect the Pride Lands while they're gone.
Prince Kion takes one final look back at his homeland before giving a reassuring smile and leaving in search of the healing he and Ono need.