The film begins with two prologues, the first during the war between the tribes. Bashenga is shown praying to Bast, offering his own life in exchange for his tribe's protection. Moved by his selflessness, Bast*(voiced by Sophie Okonedo)*appears to him and directs him towards the heart-shaped herb. After the Marvel logo, the second prologue is just after the climax of the first film, showing W'Kabi being judged by the council. Despite M'Baku suggesting he be put to death, T'Challa sentences W'Kabi to life imprisonment.
Three years later, Wakanda continues to provide aid and resources to the rest of the world following the invasion in*Infinity War. T'Challa goes to America to speak to the Avengers (a meeting that is not shown onscreen) and Ayo is made to accompany Shuri with her lab work while Okoye goes with T'Challa. When in Shuri's lab, Ayo finds designs of a female-fitting Black Panther suit, and Shuri eventually convinces Ayo to train her as a warrior.
Meanwhile, at the Oakland outreach centre Nakia is approached by a former Wakandan watchdog named Achebe (Wesley Snipes)*who reveals that he is her long-disappeared father. He explains that he and her now-dead mother left with T'Chaka when she was only a child to find a "special treasure", but T'Chaka returned alone when they both disappeared. Nakia brings him to T'Challa and they accompany him and Okoye back to Wakanda.
When they return, Shuri reveals that she has been trained by Ayo and wants to help T'Challa to defend Wakanda. T'Challa is reluctant, though Okoye suggests that Shuri take part in the annual coming-of-age ceremony at Warrior Falls.
A horrified Ramonda orders Achebe to be imprisoned without Nakia's knowledge. When T'Challa questions her, Ramonda reveals that Achebe disappeared because he tried to betray T'Chaka, feeling that his bloodline was more deserving of the throne. When she learns of his imprisonment, Nakia visits Achebe, who confirms Ramonda's story, but claims that T'Chaka murdered her mother before trying to kill him as well.
Filled with blind fury at this revelation, Nakia is convinced by Achebe to kill a member of T'Challa's family as retribution, or "a life for a life". Two days later, at the ceremony, Ayo proudly wishes Shuri luck and gives her one of her favourite daggers as a token. To everyone's shock, Nakia arrives armed with Achebe's sword, challenging Shuri to ritual combat.
To T'Challa's concern, Shuri accepts the challenge. She initially fights unarmed, instead trying to dodge Nakia's attacks, but Nakia eventually injures her with the sword, showing Shuri and the others that she is indeed fighting to kill. Shuri pulls out Ayo's dagger and they struggle, with Nakia keeping the upper hand throughout. She beats Shuri down at the edge of the waterfall, but Shuri is able to dodge her last attack, causing Nakia to lose her step and fall from the edge, presumably dead.
As Ayo comforts a traumatised Shuri, T'Challa asks the Jabari to search downriver for Nakia's body, though they cannot find her. Nakia, having barely survived, sends her father a means to escape as they plan to find the treasure he was banished searching for. On his way out, he releases W'Kabi and brings him along, claiming to be his "path to redemption". On his way out, Achebe traps T'Challa in the throne room, exposing him to a gas version of the serum that nullifies the powers of the herb.
After W'Kabi and Achebe escape, T'Challa and Shuri search their father's archive to discover an ancient map. The map leads to the original garden of Heart-Shaped Herbs, which Bashenga built a sacred temple around in honour of Bast. Ramonda confirms that this is the treasure Achebe seeks. Seeing this as the last chance to restore his powers and preserve the legacy of the Black Panther, T'Challa decides to find this garden and he and Shuri set off with M'Baku and the Dora Milaje to get to it.
W'Kabi and Achebe rendezvous with Nakia in the jungle and they begin to walk on foot to the temple. Half a mile away from it, they discover a single herb that Achebe convinces Nakia to eat, enhancing both her strength and temper as she radically alters her Wakandan clothing to resemble*her comic outfit.
Meanwhile, T'Challa's group arrive at the temple and enter it, finding the sacred garden. Shuri immediately picks up a herb and plans to take it, though T'Challa still remains adamant that she is not ready for it. The intense argument leaves with Shuri storming out, taking the herb with her. After she leaves, T'Challa takes a herb and awakens in the Ancestral Realm, where he meets T'Chaka and the other kings.
When T'Chaka mentions that the garden must be kept away from Achebe and Nakia, he is confronted by the spirit of Erik Killmonger. T'Challa and Killmonger have an intense debate whether or not he will have to kill the woman he loves for the greater good, a sequence that will probably look quite trippy and symbolic with the actual landscape around them being altered similar to "Be Prepared" in*The Lion King. T'Challa finally decides he does not wish to kill her, and to his surprise Erik accepts his decision. He and Erik have some humorous banter where Erik admits that T'Challa probably will be a better king than he was, giving T'Challa a form of closure for killing Erik.
As he awakens, M'Baku warns him that the enemies are on their way. Shuri arrives to help, both she and T'Challa activating their suits with the power of the herb. The siblings fight Nakia as W'Kabi fights Okoye and M'Baku while the Dora Milaje fight Achebe. T'Challa spares Nakia, but she attacks him and is thrown into the water.
Nearly unconscious, she awakens in the Ancestral Realm and meets her mother*(Viola Davis). Her mother reveals that Achebe was the one that killed her, prompting Nakia to wake up and brutally beat Achebe. T'Challa and Shuri's suits accidentally activate an energy explosion, causing the temple to become unstable as a fatally wounded Achebe sets fire to the rest of the herbs.
As the temple begins to collapse, Ayo pilots the ship in to rescue them, with M'Baku and the Dora Milaje lowering a chain for them to grab onto. As they begin climbing, Achebe also latches onto the chain behind them, causing T'Challa to fall off of the chain. He is grabbed by W'Kabi, whom Achebe sadistically orders to kill T'Challa. As the jet begins to get weighed down, W'Kabi sacrifices himself and lets go of the chain to tackle Achebe, causing them both to fall into the exploding temple to their deaths as the jet escapes with the others unharmed.
As they land outside the rubble, the group mourn W'Kabi and T'Challa laments that he and Shuri will be the last Black Panthers. Shuri confidently disagrees, revealing that she saved a single herb before the fire. When they get home, she studies the herb and recreates the properties, allowing them to replicate the plant.
A year later, a new garden is thriving in the kingdom, ensuring the legacy of the Black Panther will live on. In the final scene, T'Challa waits at the edge of the border, where Nakia arrives to meet him. She reveals that she cannot stay in Wakanda as his Queen, feeling remorse for her actions committed under her father's influence. However, she states that she will always wait for the day that he no longer needs to be King or Black Panther, and the two share a kiss and a goodbye, both confident that they will meet again.
