In 1970, Nicholas Garrigan graduates from the University of Edinburgh Medical School. With dull prospects at home, he decides to seek adventure abroad by working at a missionary clinic in Uganda run by David Merrit and his wife, Sarah. Garrigan becomes attracted to Sarah, who enjoys the attention but refuses to engage in an extramarital affair. After Garrigan arrives in Uganda, General Idi Amin overthrows President Milton Obote in a coup d'état. Amin gives a well-received speech, but Sarah is pessimistic. Garrigan is called to a car accident involving Amin and treats Amin's hand. During the incident, Garrigan takes a gun and shoots a mortally wounded cow when no-one else is willing to perform euthanasia. Initially hostile to Garrigan, Amin warms up to him after discovering he is Scottish due to his xenophilia for the Scots. Delighted by Garrigan's initiative, Amin exchanges clothing with him and subsequently invites Garrigan to serve as his personal physician and lead efforts to modernise the Ugandan healthcare system.
While working for Amin, Garrigan becomes a trusted confidant and is entrusted with a wider range of duties, include matters of state. Despite being dismayed by acts of government repression, Garrigan accepts Amin's explanation that cracking down on political opposition will bring lasting peace to Uganda. Garrigan eventually learns that Amin has ostracized the youngest of his three wives, Kay, because she has given birth to an epileptic son, Mackenzie. When treating Mackenzie, Garrigan and Kay start to form a relationship. Eventually, Garrigan becomes disillusioned by Amin as he witnesses increasing amounts of paranoia, murders and xenophobia. He attempts to announce his intention to return home, but is rebuffed by Amin. While at a party, after doing his best to evade a go-go dancer who is assigned to become his lover, he and Kay have sex, and she says he must find a way to leave Uganda. Amin secretly replaces Garrigan's British passport with a Ugandan one to prevent him from escaping, which leads Garrigan to seek help from Stone, the local Foreign Office representative. Garrigan is told by Stone he will be secretly transported out of Uganda if he assassinates Amin, which Garrigan refuses.
In 1972, Amin orders the expulsion of Asians from Uganda over Garrigan's protests. This creates a labor shortage that tanks Uganda's economy. Kay informs Garrigan that she has become pregnant with his child. Aware that Amin will murder her for infidelity if he discovers this, she begs Garrigan for a secret abortion. Delayed by Amin's command that he attend a press conference with Western journalists, Garrigan fails to meet Kay at the appointed time. Kay concludes she has been abandoned and seeks out a primitive abortion in a nearby village, where she is apprehended by Amin's forces. Garrigan finds her dismembered corpse on an autopsy table. Distraught, he decides to kill Amin. A hijacked aircraft is flown to Entebbe Airport by pro-Palestinian hijackers seeking asylum. Amin, sensing a major publicity opportunity, rushes to the scene, taking Garrigan along. At the airport, one of Amin's bodyguards discovers Garrigan's plot to poison Amin under the ruse of giving him pills for a headache. Garrigan is beaten by Amin's henchmen before Amin arrives and discloses he is aware of the relationship with Kay. As punishment, Garrigan's chest is pierced with meat hooks before he is hanged by his skin.
Amin arranges a plane for the release of non-Israeli passengers, and the torturers leave Garrigan unconscious on the floor while they relax in another room. Garrigan's medical colleague, Dr. Junju, takes advantage of the opportunity to rescue him. He urges Garrigan to tell the world the truth about Amin's regime, asserting that the world will believe Garrigan because he is white. Junju gives Garrigan his own jacket, enabling him to mingle unnoticed with the crowd of freed hostages and board the plane. When the torturers discover Garrigan's absence, Junju is killed for aiding in the escape. The Entebbe incident irreparably ruins Amin's reputation in the international community, and in 1979 he decides to invade Tanzania, which counterattacks and captures Kampala, overthrowing him. He lives the rest of his life in exile in Saudi Arabia until his death in 2003.
