A REAL-LIFE political thriller that's hard-hitting, soul-searching, gut-wrenching, and sexy too, but with a conscience: that's what director Kevin McDonald daringly achieves through the device of allowing a fictional young Scottish doctor become the chance acquaintance of the terrifyingly charismatic Idi Amin, a one-time boxer and soldier who charmed his way to power as President of Uganda in a 1971 coup against the corrupt Milton Obote. "I know who you are and what you are, " Amin told cheering crowds. "I am you."

Think of The Last King of Scotland as a gripping cautionary tale of how easy it is - often by doing nothing - to become complicit in the regime of a psychopathic tyrant. Western politicians do it all the time, for their own devious reasons, Neville Chamberlain with Adolf Hitler, Richard Nixon and Henry Kissinger with General Pinochet, Donald Rumsfeld with Saddam Hussein, so it's no wonder many ordinary people fall into the trap. Millions must have known about the death trains in Nazi Germany, but preferred to look the other way. Spanish tourism came of age during the heyday of Franco's dictatorship. So who could blame Nicholas Garrigan (James McAvoy), fresh out of medical school and in his first job giving injections to barefoot children at a Ugandan mission - that's when he's not jumping into bed with the resident doctor's bored wife (Gillian Anderson) - for being seduced by an offer to become Amin's private physician following a bizarre accident in the bush involving the president's speeding Maserati and a wayward cow.

After all, didn't the British Foreign Office, who helped put Amin in power, describe him as "a splendid type and a good football player."

Garrigan is so enthralled by the perks of power and by Amin's good humour - Forest Whitaker at his most mesmerising - that he doesn't want to notice the kidnappings, assassinations and atrocities around him as Amin's megalomania turns Uganda into a vast killing field. He even embarks on an affair with Amin's out-of-favour third wife (Kerry Washington). When he does wake up, it's too late. He has no way out. McAvoy, if you like, is a Scottish version of the Ugly American, a privileged white man who sows his wild oats amid the misery of the Third World's poor and oppressed - and then moves on.

McAvoy's brilliance is to drag you into this over-the-top indulgence so you share his bemused pleasure in the colourfulness of it all and in the exhilaration of being Amin's confidante. When it all starts falling apart, you're so caught up in his nightmare you even empathise with him, if somewhat guiltily.

Based on a novel by Gilles Fadden - the title is a reference to Amin's quaint addiction to all things Scottish - and directed by McDonald, until now better known for his Munich Olympics documentary One Day In September and the mountain climbing docu-drama Touching The Void, The Last King Of Scotland is a rare movie about Africa that doesn't have a white hero helping natives who by implication are incapable of helping themselves. The only real hero - much like the hotel manager in Hotel Rwanda - is a black doctor who tries to smuggle Garrigan out of the country under cover of Amin's involvement in a passenger plane hijacking crisis, saying, "Go home and tell the truth about Amin, they will believe you because you are white." By then we realise that if Garrigan does get out, he'll probably do nothing.