Swaggering and lumbering, fickle and childish, Tobi Bamtefa thunders between laughter and malice as the former Ugandan dictator Idi Amin in this adaptation of Giles Foden’s novel, directed by Gbolahan Obisesan. The president’s greed and gruesome misogyny glisten like beads of sweat under the weight of his charm and bravado. But even this confident lead performance can’t rescue a stodgy, overwritten script and humdrum production in which tensions fizzle, plot holes reign and actions lack consequence.

Daniel Portman plays Nicholas Garrigan, a fresh-faced Scottish doctor thrown into the position of Amin’s personal physician. A chirpy, stuttering romantic, he chooses to see the new president as a beacon of hope for the country. But Garrigan’s intentions are never clear. With Amin’s charm so immediately overshadowed by his brutality in Steve Waters’ altered timeline, we don’t understand why the wilfully ignorant and quickly complicit doctor is so enamoured with the president; he has to turn a blind eye so fast he’s left spinning on the spot for the rest of the show. With his ethics bludgeoned too soon, his cowardice is amplified and our sympathy for him is significantly reduced.

Bamtefa with Daniel Portman as Dr Nicholas Garrigan. Photograph: Helen Murray

Waters nudges some elements of the story closer to historical fact, making it Garrigan’s colleague Peter Mbalu-Mukasa (played with radiating anxiety by John Omole), rather than Garrigan himself, who falls for Amin’s second wife Kay (an admirably composed Akuc Bol). It is in their desperation for an under-the-table abortion that we really feel the fear of Amin’s regime for the first time. The violent wider context is otherwise laid out in unimaginatively structured international news bulletins. Meanwhile, Garrigan’s love life is reduced to his trying to kiss a British diplomat’s wife on a flaccid fishing trip, a scene so unnecessary you wonder if they were just trying to fill time.

This story of coups, protests and torture hardly lacks drama; it should feel epic. Yet it plods. When the last half hour takes a baffling turn into play fights and school-style narration, the action begins to feel as flimsy as the plastic severed limbs that scatter the stage. The Last King of Scotland boasts solid performances, and it is a show clearly concerned with complicity, but ultimately it fails to get us on side.