It's the beginning of the 1970s and newly graduated doctor Nicholas Garrigan (JAMES McAVOY) not only wants to get out from under the shadow of his Scottish father but also is desirous of making a difference in the world. Accordingly, and with a choice spin of a globe, his journey leads him to Uganda, where he provides medical services in a remote village working with Sarah Merrit (GILLIAN ANDERSON) and her husband who's often gone for long stretches of time.
The idealistic Scot becomes enamored with her, but she's reluctant to reciprocate. Besides, the would-be romance is cut short when they're summoned to tend to Ugandan President Idi Amin (FOREST WHITAKER) who recently successfully orchestrated a military coup to take control of the country. The charismatic leader is immediately impressed with Nicholas' spunk and lack of pretense, and thus offers him the position of his personal physician.
Initially reluctant, Nicholas finally agrees and soon becomes wrapped up in Amin's world that includes supplanting Jonah Wasswa (STEPHEN RWANGYEZI) as the President's closest advisor. He also meets and befriends one of the leader's wives, Kay (KERRY WASHINGTON), the hidden but well cared for mother of some of his children. Then there's local British official Stone (SIMON McBURNEY) who wants Nicholas be his informant, but the doctor has become so caught up in the power and moment that he doesn't pay heed.
Yet, after an unsuccessful attempt on Amin's life, the dictator becomes increasingly paranoid about everything and everyone, including Nicholas. Considering that and with rumors about widespread murders, the doctor finds his situation in the inner circle changing in ways he couldn't have imagined.