Certain plays are monstrously hard to review because they contain a development that can’t be foreseen and governs all that happens thereafter yet should not be revealed. You might think that a play about the last night on Earth of Martin Luther King Jr would not belong in this category. After all, Katori Hall sets her play in King’s suite at the Lorraine Motel in Memphis, Tennessee, where at 6.01pm the following day — April 4, 1968 — he will stand on the balcony to greet a crowd and be shot dead.

We know this before the play begins and nothing the author can do will alter it. Yet Hall’s carefully crafted plotline contains a jolt so unexpected that it shifts our understanding of what happened previously as well as what will follow.

I’ll have a go. We start in a thunderstorm — brilliantly realised by Dick Straker’s projection design — and are taken from there straight into the fateful motel room. King arrives after delivering what will be his last speech, the one where he refers to himself as a latter-day Moses seeing from a mountaintop the Promised Land he is fated not to enter.

The sense of violent death pervades the play. David Harewood’s King, in a superbly realised performance, flinches at every thunderclap. There has been a threat to blow up the plane that brought him to Memphis. Every day he is an assassin’s target.

The coffee he orders from room service is brought to him by Camae, a sassy and engaging young black woman played (in an eerie coincidence, given the setting) by Lorraine Burroughs. Their interaction, teetering on the edge of flirtation, she cheeky, he intrigued, is fascinating, convincing and packed with fun.

The jolt comes when Camae accidentally reveals that she knows something about King’s childhood no ordinary person could know. So is she an FBI spy sent to entrap him? Or someone not so ordinary?

What follows is a gripping exploration of a man’s emotions as his inevitable death comes into view. He has a task to finish, a family to care for — and Harewood judges with a fine precision the phone call King makes to his daughter. He also captures the orator’s occasional vibrato in his vowels, so that we can recognise him as what Camae calls “a pulpit poet”. He makes heart-rending the desperation — and fear too — at a life’s work left unfinished.

The performances in James Dacre’s fluent production strike me as faultless — with Harewood and Burroughs balancing tension with humour, and matters of great moment with the smaller stuff of life.

The author grew up in Memphis, a child of the post-civil rights era who benefited from the changes King could only glimpse from his mountaintop. She and her creative team have honoured his memory in this powerful play.

Box office: 020 7-978 7040, to July 4

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