Spoiler
They write out T'Challa at the beginning of the film, suffering from an unspecified disease his sister Shuri attempts desperately to cure by recreating the "Heart-shaped herb", but fails to do. Not really sure why she thinks this would cure him. This is what gives the Black Panther his powers, it's already in him. Why would giving him more cure him? Unless the herb is the cause and one has to keep taking it every so often to prevent from getting sick? But the movie doesn't explain it. At any rate, jumping a year later, Wakanda is on the defensive now that the world knows they have Vibranium and their King is gone. However, another source of Vibranium is detected under the Atlantic Ocean, which the Talokanil (to avoid confusion with DC's Aquaman, they aren't Atlantians in the MCU, with their culture instead based on Aztec mythology) kill to miners attempting to extract it. K’uk’ulkan (Namor to his enemies) then goes to Wakanda and asks that they find the scientist (Riri Williams) who developed the Vibranium detector, as by revealing themselves as a society with Vibranium based technology, they've also opened up Talokan to being discovered and attacked.
We find out the Talokanil Aztec ancestors all ate a plant similar to the Wakandan "Heart-shaped herb" in hopes it'd help them against the invading Spanish in the 1500's. It transformed them, making their skin blue and made it so they couldn't breath air, forcing them to live under water where they built a new society of their own, similarly to Wakanda, all based on the use of Vibranium. We're also told, Namor's mother was pregnant with him at the time of her transformation, which resulted him being born a mutant. I have to say, I really liked this origin for Namor and his people.
The Talokanil and Wakandans end up fighting each other, resulting in Queen Ramonda. Using some fibers from the Taloka plant, Shuri recreates the "Heart-shaped herb" and becomes the new Black Panther, intent on killing Namor. To help out, Riri builds herself a new advanced armor with Wakandan technology. But at the last moment, Shuri decides not to kill Namor, offering him an alliance instead in order to avoid endless war between the two nations. Namora is pissed that he'd yield, but he tells her when Wakanda is eventually attacked by the surface world, they'll turn to Talokanil for help, giving them the opportunity to conquer the surface world. Riri is allowed to return home, but she isn't allowed to keep her new armor.
In a mid-credits scene, Nakia reveals to Shuri that she had a son, Toussaint, but his Wakandan name is T'Challa, in honor of his father. Nakia explains she and T'Challa wanted him to be raised away from the pressures of the throne.
We find out the Talokanil Aztec ancestors all ate a plant similar to the Wakandan "Heart-shaped herb" in hopes it'd help them against the invading Spanish in the 1500's. It transformed them, making their skin blue and made it so they couldn't breath air, forcing them to live under water where they built a new society of their own, similarly to Wakanda, all based on the use of Vibranium. We're also told, Namor's mother was pregnant with him at the time of her transformation, which resulted him being born a mutant. I have to say, I really liked this origin for Namor and his people.
The Talokanil and Wakandans end up fighting each other, resulting in Queen Ramonda. Using some fibers from the Taloka plant, Shuri recreates the "Heart-shaped herb" and becomes the new Black Panther, intent on killing Namor. To help out, Riri builds herself a new advanced armor with Wakandan technology. But at the last moment, Shuri decides not to kill Namor, offering him an alliance instead in order to avoid endless war between the two nations. Namora is pissed that he'd yield, but he tells her when Wakanda is eventually attacked by the surface world, they'll turn to Talokanil for help, giving them the opportunity to conquer the surface world. Riri is allowed to return home, but she isn't allowed to keep her new armor.
In a mid-credits scene, Nakia reveals to Shuri that she had a son, Toussaint, but his Wakandan name is T'Challa, in honor of his father. Nakia explains she and T'Challa wanted him to be raised away from the pressures of the throne.
Overall, I enjoyed the film, despite a few bits that could have been improved upon.