It's a brave project, this one: a one-man adaptation of Joseph Conrad's 1899 novella, which exposes the exploitation of indigenous peoples in the then-uncharted Belgian Congo.  The scene is set with an intriguing opening monologue, reminding us of the days when European empire-builders ruled the world – and, very pertinently for this particular story, when much of the map of central Africa was still blank.  As Marlow, the story's young narrator, steams up the Congo River in pursuit of valuable ivory, he finds himself enmeshed with an unexpected nemesis: an embodiment of colonial avarice, the hated Mr Kurtz.

The historical framework for Conrad's tale is impossible to ignore, and the adaptation does retain references to "half-castes" and "savages" which sound profoundly troublesome to modern ears.  But, although narrator Marlow employs the racist terminology of his time, he is not fundamentally a racist man.  He shares our shock at what he finds in Africa – particularly in one brief but haunting scene, when he discovers an exhausted labourer who's crawled away to die – and actor Guy Clark delivers a quietly convincing portrayal of Marlow's gradual decline, growing angrier and more desperate as the truth about the colonial adventure is slowly revealed.

Yet at the same time, Scandal and Gallows Theatre build an atmosphere of menacing otherness, a sense that Marlow truly is travelling through dangerously unknown lands.  The frequent lighting changes grow distracting after a while, but the sound design is both delicate and highly effective: as we hear the noises in the night surrounding Marlow's small boat, we understand both the vastness of the African forest and the fragility within it of even heavily-armed men.  Clark ably carries the audience through the highs and lows of the script, as Marlow's mood switches between excitement at exploration and horror at the reality of what he finds.  And Maddie Skipsey's direction adds some simple, effective staging too; three large packing-trunks become a ship's rail, a deathbed, or the elevated seat of an imperious colonial functionary.

It's a pity, then, that I never felt the sense of time and distance that such an epic journey demands.  The simplest of devices – perhaps a map in the background – could have helped here, aiding my understanding of how far Marlow has travelled and just how long he's been away from home.  And with a linguistically-complex script and a fast-paced performance, the simple act of keeping up with the plot also demanded a little too much of my attention; perhaps as a result, the creeping, all-pervading misery engulfing Marlow didn't have quite the emotional impact it could or should have done.

While playwright George Johnston has done good work simplifying Conrad's original story, I'm left wondering if Heart of Darkness was just too much to chew on.  Condensing a novella to an hour-long Fringe show is a challenge under any circumstances – and here, the situation's complicated by the need to address the outdated worldview which underpins the original text.  But it's an impressive performance from Clark, who captures distinctive personalities with ease, and has the physicality he needs to keep a wordy solo show engaging.  Overall then, Scandal and Gallows deliver an effective show this time round, and offer plenty of promise for the future too.