Opening the film T'Challa falls terminally ill and passes away as a result of Shuri failing to recreate the Heart-Shaped Flower using her DNA splicing technology. This causes Shuri to shun Wakandan culture and commit to technological advancement for Wakanda's future problems.
One year later, the French sends a group of mercenaries to try and invade and seize Wakandan vibranium. However, they are stopped by the Dora Milaje.
This causes a court dispute over Wakanda hoarding vibranium, however Wakanda does not want to give away vibranium. Queen Ramonda notes that it can be used to create extremely powerful, and dangerous, technologies. Something she fears the rest of the world will do.
Since Wakanda refuses to distribute vibranium to other countries, the CIA and US Navy seize and use a vibranium detector to search for vibranium elsewhere. They successfully locate vibranium in the Atlantic Ocean, but they are killed by an unknown threat while confirming the findings.
This leads to rapidly rising tensions between Wakanda and the rest of the world. People assume that Wakanda is killing people who are searching for vibranium, while Wakanda begins grappling with the fact there is vibranium elsewhere in the world.
While grappling with the rapidly rising tensions and grief over the loss of T'Challa, an individual by the name of Namor speaks with Wakanda on the behalf of the Talokanils, a hidden civilization that has lived underwater and also has an abundance of vibranium. Namor demands that Wakanda hands over the scientist who designed the vibranium detector, and threatens Wakanda with war if they refuse or fail.
Shuri and Okoye search for person who created the vibranium detector. This person is Riri Williams, an MIT student. The two, on behalf of Wakanda, choose to not turn her into Namor but rather attempt to bring her to Wakanda.
However, Shuri, Okoye, and Riri are intercepted by both the FBI and Talokanils. Despite their vibranium weaponry and Riri's Iron Heart Suit, Shuri and Riri are captured by the Talokanils and brought to Talokan. Desparate to get her daughter back, Queen Ramonda reaches out to Nakia to infiltrate Talokan. She lures Namor out with a false promise, while Shuri, Nakia, and Riri escape to Wakanda.
As a result of the betrayal, Namor launches an attack on Wakanda. In a show of physical and technological dominance, Wakanda falls and Queen Ramonda is killed.
Finally ready to accept the cultural importance of the Black Panter and assume her role as leader of Wakanda, Shuri is successful in recreating the Heart-Shaped Flower. She dons Killmonger's former suit, who was the antagonist of the previous movie, and prepares Wakanda for retalliation on Talokan.
In preparation for the final showdown against Namor, Wakanda develops a lot of new technology, such as the finalized Iron Heart suit, the Midnight Angel suits, an aircraft that contains radiators (to "dehydrate" Namor), and giant ship that uses sonar waves from the vibranium detector to detract enemies underwater.
Wakanda fights the Talokanils on the ocean, managing to get Namor into the radiated ship. However, he quickly blows it up, ultimately ending up battling Shuri in a desert.
With the strength of the Black Panther and the words of her brother, Shuri is able to defeat Namor. Namor soon concedes and agrees to stop trying to wage war on the outside world. In return Shuri will keep Namor's people safe.