I found this on reddit, this is the link:
https://www.reddit.com/r/MarvelStudiosSpoilers/comments/7vu8nc/black_panther_full_plot/
I've copied and pasted it below
Right
Itll be too exhausting detailing the whole plot but Ill point it out in bullets:
Black Panther happens right after Civil War
Theres a recap in the beginning that shows the five tribes uniting to be Wakanda and explaining why they have hid their identity from the world. They also showed this flower that gives the Black Panther unlimited strength.
Flashback to 1992 in Oakland, CA. Sterling K. Brown is the baby brother of TChaka and he works as an operative in the US. He wants to bring Wakandan weapons (which we know are powerful and more advanced even compared to Tony Starks) to their people since they are always the one thats being oppressed. Hes accompanied by a friend who also turns out to be a Wakandan spy. Long story short, TChaka doesnt want him to continue with his plans and ends up killing him.
Flashback to present day and TChalla prepares to be crowned as king, but has to get approval from each tribe. If one tribe doesnt approve, they have one warrior who must fight TChalla. One wins when the other yields or dies during combat. MBaku from the Mountain Tribe challenged TChalla but of course he eventually wins tough he still has doubts about being king.
Were introduced to Nakia, TChallas ex, who works as an operative. She left Wakanda to go help people who are oppressed. Okoye heads the Dora Milaje I think theyre the most badass group of women Ive seen. Theres also WKabi, TChallas friend from another tribe, then Shuri, TChallas tech-savvy sister, and Queen Ramona.
For his first duty as king TChalla decides to go after Ulysses Klaue, who his father has failed to capture in the last 30 years. - WKabis parents were killed by Klaue and wants to join in capturing him but TChalla said that its best to stay there and protect the people. WKabi made TChalla promise to either take Klaue to stand trial or kill him as revenge for his parents death. They learn that hes selling vibranium to a criminal group in Busan, South Korea so Nakia, Okoye and TChalla head there to capture him. The vibranium Klaue was selling was stolen from a London museum where he was aided by Killmonger.
Inside the underground casino in Busan, TChalla finds Agent Everett Ross and learns theyre there to capture Klaue as well (Stan Lee cameo). Big action scene comes up once Klaue realizes it was a setup. Thats where a bulk of the action scenes happen just like what you saw in the trailer.
When Klaue was taken in for questioning by Ross, he reveals the truth about Wakanda and he starts doubting if Wakanda is really a third world country.
Before TChalla could explain Erik bombs the place and ambushes everyone and rescues Klaue. Ross was shot in the spine trying to protect Nakia. TChalla decides to bring him to Wakanda so they can save since he considers Ross as a friend.
Erik tells Klaue that he wants to go to Wakanda but Klaue wants to just runaway. Erik kills Klaue and flies to Wakanda by himself, bringing Klaues body with him.
When TChalla returns to Wakanda they manage to save Ross through Shuris vibranium tech. WKabi was disappointed when TChalla says that Klaue got away. WKabi was then surprised to see Erik as he arrives to Wakanda brining in the body of Klaue.
Erik then reveals hes the son of Sterling K. Browns character (baby bro of TChaka). Hes seeking revenge for the death of his father and wants Wakanda to start helping people in poorer countries, particularly people of their kind because its always them whos always in the minority.
Since Erik is the son of the Kings brother, he has a right to the throne so as rule they have to do the combat challenge again to prove who the worthy king is. They fight and TChalla loses and falls off a waterfall, seemingly dead.
Erik is crowned the new king, and orders all the flowers (the one that gives special powers) to be burned. He then instructs everyone to start shipping Wakandan weapons to other countries, something that Shuri and Nakia hope to stop. Okoye wants to help, but shes bound by her duties to protect the throne whoever sits there.
Nakia manages to get one more flower before everything was burned, and heads with Shuri, Ross, and Queen Ramona to MBaku. They offer him the flower and ask that he should challenge Erik. MBaku then shows them TChalla, whos been rescued and in recovery. They give him the flower where he gains his powers and Shuri gives him his Black Panther suit.
Shuri, Nakia and TChalla go to stop Erik from shipping the weapons while Ross (who was an ex-pilot) flies in VR (like what Shuri did in one of the Black Panther clips) to destroy the ships before they can leave Wakanda.
WKabi sides with Erik and fights TChalla with his army. The Dora Milaje decide to help TChalla. Long battle ensues until TChalla and Erik are now fighting one-on-one.
TChalla eventually stabs Erik and as hes accepting defeat, he tells TChalla that his father always tells him that Wakandan sunsets are the best in the world. TChalla takes him to the top of the mountain where Erik sees the sunset and then dies.
TChalla finally realizes his purpose and asks Nakia to get back together. Wakanda Forever!
THE END.
First post-credits scene: TChalla heads to the United Nations committee and eventually reveals the truth about Wakanda.
Second post-credits scene: Bucky is now awake from Cryo and Shuri tells him something (forgot what she said). Bucky looks on the horizon it looks like the same area where the battle happens in Infinity War.
Last text appears: BLACK PANTHER will return in AVENGERS: INFINITY WAR