Originally penned by Joseph Conrad in 1903, Heart of Darkness deals with the deepest, most dangerous misunderstandings between human beings. Set during the era of imperialism, ship’s captain Charlie Marlow relates to his London dockyard comrades a disconcerting tale of a journey to the heart of an African jungle. As Alan Oke’s Marlow moves between the present and the voyage, evil ivory dealer Kurtz dominates the narrative. His atrocious world is a darkness that removes the illusion of glorious empire (as imperialists of Conrad’s day would have perceived it) and replaces it with a disturbing place of savage violence and unregulated pillaging. This is a pre-globalised world where foreign shores represent otherness and complete unknowns – quite a challenge for the modern-day librettist and composer and one that they tackle with some success.

Oke does well to arouse our curiosity of the ‘remarkable man’ Kurtz, but is not the most compelling performer, either vocally or dramatically. That accolade must go to Morten Lassenius Kramp as Kurtz himself, who gets to utter the chilling dying phrase ‘The Horror, the horror’, (familiar to those who have seen Apocalypse Now and inspired by Conrad’s original). He appears near the end of the opera, dying and drooped across the desk on the ship’s deck, his fine physique smothered in what looks like blood. As his ghoul-like body writhes, his earthy Bass holds the audience in thrall. Towards the end, the story loses its momentum and we appreciate all the more the appearances of Sipho Fubesi’s Manager / Company Secretary and Paul Hopwood’s Helmsman / Accountant.

Tom Phillips’s libretto draws exclusively from Conrad’s novella. But the greatest departure Phillips makes from Conrad is the fact that the audience can see Kurtz in his physical form on stage, rather than relying on the narrator’s memory. This added possibility in the operatic interpretation breaks the total otherness of Kurtz’s enigma - and it works. The physical manifestation of this unnatural creature of a man, distant from reality and tribal in appearance, powerfully represents the frightening combination of madness and power that is Kurtz’s symbol of brutal imperialism. Those infamous last words resonate, before a blue light on his body confirms that he has finally died.

Kurtz’s figure is a little incongruous with the rest of the performance and his derangement is unconvincing for one so apparently all-conquering. His feral appearance heralds a move towards the bizarre and mock-tribal that becomes rather uncomfortable and it is difficult to conceive his relation to his fiance. Granted, the maddening effect the tropics are said to have on visitors is reinforced, but Kurtz is a visual crudity in an otherwise subtle and efficient staging. Lighting is used effectively to pick out characters and create alarm when the ship of Marlow’s narrative is attacked; and the fact that past and present are played out on one boat succeeds in conveying the fact that Marlow carries the experience with him in his psyche. The boat deck (built outside the ROH by Setup Scenery in Cambridge) is simple but effective, resting in shallow water under a vertical cat’s cradle of ropes. When an eerie recorded voice sings out of the darkness that symbolises our innermost fear of the unknown, the sense of that fear is palpable.

And what of the music? Fluid, urgent and anxiously dissonant, but altogether patchy, there are memorable moments. It isn’t quite as fine as O-Regan’s 2010 Latent Manifest, despite appearing in an updated version from 2008, but there are wonderful orchestral touches. Near the climax, clarinets and flutes trip over each other in a fleeting burst of layered rhythmic interest, and O’Regan has perfected the art of allowing the ensemble to function as a giant percussive instrument in choppier moments of tension. Otherwise, vocal lines are well shaped but not always memorable (or aria-like, typically of many contemporary operas). Also the libretto sometimes falls clumsily upon what could be called recitative, notably in the case of Jaewoo Kim’s Harlequin. But Chroma Orchestra, under Oliver Gooch, equip themselves admirably, their timbre maintaining a wonderful bite.

Overall Philips and O’Regan’s Heart of Darkness treats a sinister and multi-layered subject with imagination and artistic flair and the small cast impressive. It’s a little too long for a one Act opera, but perhaps as thought-provoking and successful as any adaption of Conrad’s symbolic frame-narrative can be.