“How’s mum?” Daniel asks his brother for the third time, or maybe it’s the fourth, or then again, it could be the fifth time, or is it the first time after all? New Celts writer Cameron Forbes’ Besides the Obvious relies on these surreal shifts of time and mind, mixing absurdist Beckettian language games with the quiet menace of Pinter to create a piece of promising, if eventually deflated, piece of new writing.

The premise is innocent enough. Successful sharp-suited lawyer Eddie (David Edment) visits his down-and-out photographer brother Daniel (Sean Langtree) for a cup of tea and catch up. Eddie is a hard-working lawyer, the “and son” of the family firm and firm favourite – or not. Maybe sister Kim’s the favourite, Kim who has left, Kim who wants to leave, etc.? Meanwhile, Daniel is a freelance photographer, currently undertaking a commission from the police to document corpses at crime scene. As you might have guessed, Eddie and Daniel do not get on.

Forbes’ script is an intricate and intriguing work – the brothers’ lives and memories converge and divide in complex patterns as anxieties loom large amongst small talk. The requisite round of niceties barely mask contained resentment as the brothers’ exchanges ricochet between petty insults and back-slapping childhood nostalgia trips. When Eddie’s assured exterior begins to dissolve, Daniel doesn’t show any mercy and an ordinary living room becomes an emotional minefield, full of quick-fire accusations and raging imprecations.

Yes, it may sound like your average domestic drama, but it soon becomes apparent this entire situation somehow exists beyond the usual borders of rationality and even human time – not a study of a siblings’ relationship but rather the deterioration of an apparently sane man’s mind. It takes (perhaps too much) dedicated attention to appreciate the subtlety of the script, which races forward, back and around again with a confidence which, if confusing, is nonetheless complimentary – Forbes clearly doesn’t feel the need to spell it out for us and it is an enjoyable challenge to piece together the narrative from what we are sparingly given. There are nicely sinister touches that reveal what really preoccupies the brothers, for they only seem to genuinely connect, laugh uproariously or come together in conspiratorial closeness when smirking at the memory of their father falling down the stairs, about broken hipbones, erotic asphyxiation and electric shocks throwing people clear across a room. A few neat staging devices hint cleverly at growing isolation and instability – for example, when Daniel offers his brother a drink but Eddie takes it out of his own jacket – a trick that works far better than the invasive and rather tacky use of siren noises to disrupt the dialogue.

Indeed, whilst the writing approaches greatness, Besides the Obvious is generally let down by an unimaginative staging. Though the actors build up a convincing rapport, attempts at naturalism end up jarring with the organised chaos of the content, and the abrupt ending erupts more into cliché than catastrophe. Let’s hope Cameron Forbes returns next year with a more cohesive piece to take a deserved place amongst Edinburgh’s most intriguing new writers.

*** – 3/5 stars

Beside The Obvious played at the Edinburgh Fringe Festival.