The Camdram blurb for Post is distinctly brief. Indeed, the concept of the one-man show, a new play by Harry Michell and Will Attenborough, is simple: Terry is a postman with a mischievous habit of opening other people’s letters. As the audience take their seats, we find Ed Eustace silently going about his postmanly business, beady-eyedly scanning the rows of pigeon holes into which he proceeds to nimbly slot each letter.

Set Designer Connie Harper’s three monolithic pigeon hole blocks give a sense of aggressive efficiency, offset by homely touches such as Eustace’s Royal Mail sweater and mug. Director Charlie Risius has clearly taken pains to ensure the credibility of the one man and one scene which make up Post, and it gives the play a solid grounding.

Eustace plays the postie with doddery humility, and a cracking Yorkshire accent that concludes every utterance with an ‘eh’, the meaning of which lies somewhere between exhalation, indifference and despair. There is something wickedly brilliant about the ceremoniousness with which Eustace opens each misappropriated letter, slicing each one open with a silver letter-knife. And yet the naughty child in him is strong: as he says himself, "Kids will be kids, until adults - and then adults will be kids".

Though working-class-hero-cum-aspiring-intellectual is a well-worn character type, Eustace brings it out in Terry with a warmth that sweeps away cliché. Perhaps it is the earnestness with which he aspires to everything: "I could have been" seems to be Terry’s refrain; with each repetition, the realisation dawns that Terry sees his life as having already been lived, as an unfulfilled potentiality.

Post is a carefully trodden tightrope between tragedy and comedy. Attenborough and Michell carve out moments of humour in Terry’s monologue, that at the same time bespeak a reflectiveness that is deeply endearing: he says he couldn’t have been a cat person because "they’re just so knowing". He moves easily between reading others’ letters and retelling his own life story, occasionally blurring the distinction between the two.

One would think that Terry might quickly begin to feel like a one-trick letter-opening pony, but surprisingly the situation doesn’t weary, as each letter adds colouring to Terry’s own persona. It slowly becomes evident that there is a profound schema to the letters Attenborough and Michell have chosen for Terry to read: the letters are in fact in dialogue with Terry’s past experiences, creating a tragic double helix that ends in the hero’s frantic search for his own lost letter.

In the play’s dramatic finale, tragedy overwhelms comedy, and we watch as Eustace undoes language, hurling letters, vomiting words and finally, emitting an unintelligible sound, something like a raspberry. It seems appropriate that Post should end on a note of childishness, for it is in the realisation that Terry is really just a big, lonely kid that the pathos of Post inheres.

Post plays at the ADC at 11pm until Saturday