Phoebe Waller-Bridge in Fleabag at the Big Belly, Underbelly.

A woman walks onto a stage, sits down on a chair and starts telling a story. Fleabag, written and performed by Phoebe Waller-Bridge, has at its heart a wonderful simplicity. With a powerful and nuanced performance from Waller-Bridge, skilfully directed by Vicky Jones, Fleabag is sure to impress at the Soho theatre, as it did with an extremely successful (Fringe First-winning) premiere at the Edinburgh Festival Fringe.

In fact, Waller-Bridge doesn’t quite walk on stage; it’s more of a semi-jog, or even a bound. The story begins with a scene certain to inspire sympathy in many, a job interview. She’s late, she’s been running. This is not a good start to a job interview and, thanks to her propensity to say and do the wrong thing, doesn’t continue well. She is that classic British favourite: an underdog. Her slightly ungainly enthusiasm is endearing from the off.

During the interview, the way in which she bluntly and excitedly proclaims things like “sexual harassment case”, or how she momentarily lifts her top, revealing just a bra underneath, before attempting to pretend that nothing has happened, cannot help but charm us, and make us eager to learn what this slightly erratic person might do next. Waller-Bridge’s ability to build a rapport with the audience is commendable, and that rapport is continued with her mastery of comic timing, suggestion and sub-text, and her expressive face with just the right amount of animation – hilariously clown-like but not grotesquely or unrealistically caricatured.

With the first scene begins our first example of the subtle but effective lighting design, by Elliot Griggs. Lighting changes accompany changes in scene and mood in such a way that supports the action, but does not detract from it. The interviewer is played by a recorded voice, sound being effectively managed by Isobel Waller-Bridge. In a one-woman show, containing numerous other characters, the times in which recorded voices were used, and when Waller-Bridge was to play the other characters herself, is an important decision. Though effective, the recorded voices are fortunately not overused, the focus remaining on Waller-Bridge’s accomplished storytelling.

The production is described as a story of “some sort of female living her sort of life”. The skill in this production lies in delivering incredibly ordinary and accessible material in a way that is utterly compelling. The rudeness is unavoidable. The ability to shock an audience is itself a notable achievement, and one wonders if the fact that is a grown woman who is being rude, describing her arguably excessive masturbatory efforts in great detail, is part of this shock. Whether the show is overly reliant on rudeness and shock tactics is debatable, but it is delivered unashamedly and unostentatiously by Waller-Bridge, and is a rare and importantly honest depiction of active female sexuality, still very much an underrepresented taboo.

Fleabag has no reservations about mixing the crude and the profound, and it is profound. It does not shy away from issues of addiction, dysfunctional relationships, violence, death and the problem of maintaining one’s self-esteem in an ever-more competitive world. And yet it remains determinedly light hearted and laugh-out-loud funny, Waller-Bridge raising a laugh with a look, or a pause. This is impressive, important, unique theatre.

Fleabag is playing Soho Theatre until 22 September. For more information and tickets, see the Soho Theatre website.