As we entered the North Wall theatre space, writer Nick Makoha was already installed stage left behind an object-scattered table, while in the gloom to stage right lurked a couple of rows of upholstered seats in a vaguely striped pattern above which was suspended a bulky shape – a heavy-duty net was it, man enough to catch and hold a sperm whale (or since this was Uganda, a Lake Victoria crocodile or two)? But no: as the lights went up, Makoha introduced his script by direct address to the audience in the form of lines of poetry illuminating the subject of enforced flight. Our two actors appeared and the play's action in Idi Amin's 1979 Uganda took our fugitive duo ever nearer to the Kenya border. And here was that hanging mass, actually a capacious roof rack, bursting with boxes and cases above the seats of a bus.

Such was the beautifully-imagined setting (designer Rajha Shakiry) doing duty for most of the 1 hour 40 mins running time (no interval), the bus seats re-arranged periodically to form chairs at a checkpoint or transport pull-up along the way, the roof luggage rack ever swaying gently in the draught of the theatre's air conditioning, nicely suggesting the bus's motion as well as disturbance of a more psychological stamp.

Our two actors played a multiplicity of characters with nonchalance: thus Akiya Henry was successively and among others a pregnant mother-of-six (of her unsatisfactory partner: "can you not marry me and then die?), a grandmother, a fiancée travelling to marry her husband-to be ("my father has paid the bride price"), a rifle-toting guard and finally a Heathrow immigration officer. Michael Balogun was now the bus drive, now its conductor, son and grandson, roadblock soldier and, often, the narrator of this quasi-road movie.

The focus was squarely on the plight of these assorted but linked characters, and I guess Makoha and director Roy Alexander Weisse were inviting us to view them both as personifications of refugees, compelled by force majeure into sudden abandonment of hearth and home towards an unknown future, and as specific victims of the seizing of the levers of power by a monstrous dictator. In the former respect, I thought the quick switches of identity by our two characters did successfully enable them to justify this seeking after a wider status. But in the evocation of the particular events in Uganda the drama was less satisfactory. I doubt whether the predominantly young audience around me managed to grasp much if anything of the nature and scale of the mayhem about to launched by this particular megalomaniac, which modern history now records.

Neither Amin himself, just once a surprisingly thin voice mouthing in the distance, nor his security apparatus were encountered beyond the occasional irruption of a standard rapacious/uncontrolled guard or two, and it was unclear to me just what precise threat had forced our citizens to decamp at a moment's notice. Nor did sound designer Durameney Kamara seize the ample opportunities here to illuminate the raison d'être for the journey and its events – the bus itself jolted along the potholed roads with hardly an engine rev let alone grinding of gears, and the sound of daily life disrupted by violence or displacement was strangely absent.

So in the end this potentially dramatic, even tragic situation, illuminated by skilful and flexible acting, was somewhat marred in its detailed realization. But I was never less than fully engaged, and the show is well worth a look this week.