“Once upon a time there was a world. And then it got fucked”. It’s a terse summary of the starting point for Paul Kennedy’s Guidelines for a Long and Happy Life, Tinderbox Theatre Company’s contribution to the 2011 Belfast Festival at Queen’s. It’s voiced by Man, one of six characters inhabiting the post-apocalyptic earth of Kennedy’s imagination, in a long, painfully intense scene culminating in the brutal rape of the bedraggled mess of a figure named Woman, who struggles doggedly across the blasted landscape of an almost totally denuded planet.

How the world actually “got fucked” in the first place is left to the imagination: it’s taken as a given that this will probably someday happen. What interests Kennedy is what comes next when human-kind is reduced to existential ground-zero. What’s left to build on when virtually everything gets wasted? Which things still matter, if any? Is the world actually worth re-building if there are still human beings in it?

For two-thirds of the play, the answers appear to be largely in the negative. A raw, inexpungible human instinct for survival keeps Man and Woman trudging onward, searching for scraps of food and company, but the attitude of both characters is grim and desperate, not hopeful. James Doran, wild and hirsute as Man, distils a rough wisdom from the little that he knows about the blasted world he is now living in, while Katie Richardson’s Woman is more openly vulnerable, inclined to trust nobody and nothing. Both act with unrelieved intensity, Doran numbingly matter-of-fact and calculating in his verbal manipulations, Richardson vividly suggesting the fearful fragilities of Woman, and the traumas inflicted on her in the lawless wasteland she now inhabits.

Together they make the rape scene properly sickening without resorting to undue histrionics or shock tactics. It’s a brutally unexpected moment in the drama, but in retrospect you see the ground being cleared for it by Kennedy’s examination of how old, settled moralities are blasted skyward in the unbrave new world of a post-cataclysmic planet – for instance, in the play’s opening section, where Ack (John Shayegh) refers to Bin (Stevie Prickett) eating human excrement when he first encountered him, and there are references to cannibalism, another taboo shattered when it’s eat or die. A fragile residue of basic human decency persists in the father-son relationship that has developed between Shayegh’s benignly practical Ack and Prickett’s more rough-mannered, animalistic Bin – but it’s a thin thread on which to hang a firmer future.

Then, unexpectedly, in the play’s penultimate section, the unrelievedly dark tone of Guidelines modulates into something seemingly brighter, transporting the audience to a neat log cabin where Colenso (Faolán Morgan) and Pleasance (Andrew Stanford) live in relative comfort, passing their time drinking coffee rations and coining the mantras referred to in the title of the play, snippets of practical advice for those attempting to survive the holocaust. Humour enters in the gentle joshing and bantering between the two characters as they distil their little nuggets of wisdom together:

“Breed as much as possible. Find a safe place and make a new home. Help one another”.

“Bury deceased bodies in a shallow grave without a coffin to help the soil and fertilise your plants”.

Morgan and Stanford adroitly catch the change of tone in Kennedy’s writing, Morgan impressing particularly with the dry quality of his comic timing, Stanford amusingly etching in the myriad of insecurities that Pleasance feels with the more intellectual Colenso beside him. More hauntingly, both actors manage to suggest the atmosphere of sheer strangeness surrounding these characters’ activities and provenance. Who are they exactly? Who asked them to write the “guidelines”? Are they the only people writing them? The Big Brother-type presence presiding over the re-emergence of humanity seems benign enough in its intentions, but already there’s a whiff of new, eerie hierarchies developing in the strangely unsettling lope of the stilted corpse operatives seen earlier shifting dead bodies into a furnace.

The cumulative effect of the final two sections is to almost magically wrest a small modicum of faith in man- and womankind’s ability to somehow renew itself after millennia of pressing frantically on the self-destruct button. It’s a gently glowing, if not exactly a heart-warming conclusion.

Director Michael Duke staged Guidelines in the Old Victor Stationery Warehouse just off the Castlereagh Road in Belfast, using its derelict, pillared expanses to shift the action from one location to another, a community “chorus” ushering spectators in torchlit darkness on each successive stage of the perambulation. The building itself felt cavernous, but Duke placed the actors within tightly confined spaces at each location, enhancing the desperate intensity of their conversations and confrontations. With sheeting rain outside the warehouse and a stiff autumn wind gusting, it was a bracingly immersive setting, physical theatre for the audience as well as the actors.

Set designer Niall Rea kept detail to a bare minimum in Duke’s tight physical spaces (only the log-cabin looked comfortingly conventional), while lighting designer Ciaran Bagnall provided mainly low-level chiaroscuro effects, in keeping with the grimness of the subject-matter. Costumes (by Susan Scott) were appropriately rough-hewn and raggedly functional, and the primeval rumblings and groanings of Justin Yang’s soundtrack underscored the action to telling effect.

Guidelines for a Long and Happy Life was one of Tinderbox’s biggest ever projects, but felt as though it could ultimately have been even bigger: seventy-five minutes seemed scarcely sufficient to do justice to subject-matter so fertile in its resonances and implications. This Belfast Festival staging was, however, unquestionably a significant achievement, an intensely thought-provoking evening, full of powerful acting and unflinching insights into the raw, primeval urgings normally sunk deep in human nature, but here, in extremis, erupting provocatively through the surface.

Terry Blain is an arts journalist and cultural commentator, contributing regularly to BBC Music Magazine, Opera Britannia, Culture Northern Ireland and other publications.