Not I, Footfalls, Rockaby, Royal Court Theatre

In many ways, the darkness is the most memorable aspect of this production. It's so deep and all-encompassing that your eyes start to play tricks on you, seeing spots of light and shadow where there is only blackness. Because of this, when Lisa Dwan's mouth is slowly illuminated eight feet up on the stage, it's easy to dismiss it at first as just another trick of the dark.

The only light in the theatre seems to emanate from the mouth itself, as it begins to gasp before tumbling into the breakneck stream of consciousness monologue that is Beckett's Not I.

First performed at the Royal Court by Billie Whitelaw in 1973, Not I is a puzzling, maddening flow of words delivered at the "speed of thought" by a disembodied mouth (pictured right). Punctuated by the occasional groan or scream, Dwan flies through the text as if it were music, accenting certain words to form the melody and allowing the rest to merge as harmony. At the end of every section, she declaims the words, "what?… who?… no!… she!…", with a chilling change of pace, before plunging back into the fray. The concept is fascinating – Beckett attempted to create the purest possible form of drama, with his words delivered straight to the audience's ears without action or distraction. Even the title denies any personal input from the performer, who is known in the text merely as "mouth". Fittingly, the final effect is more than a little discomforting to experience, and extremely uncomfortable for the actor to perform, requiring thick tar-like face make-up and straps to hold the head and body rigid above the stage.

Compared to the previous two plays, 'Rockaby' is almost soothing

In this trio of later short works by Beckett, the austere brutality of Not I is followed by the ghostly light of Footfalls, in which Dwan plays a daughter pacing along a strip of floor outside her dying mother's room. She speaks of her mother, and her mother replies as a voice-over, throaty with age. At the outset, the daughter's words are familiar to anyone who has cared for an older person – bed pans, sponge baths, injections. But soon everything is vague and reclusive, and we are left wondering whether the daughter is dead, too. Aside from the text, Dwan's movement in this piece is superb. Beckett was extremely specific in the script exactly how the footfalls of the title should be executed, and she manages to make them percussive and rhythmical without seeming forced. The lighting, too, is spectacular – designer James Farncombe has done an outstanding job of hinting at the otherworldly uncertainties of the text in the grey shafts that illuminate Dwan's progress across the stage.

The final piece in this production is Rockaby. Dwan, now attired in a black Victorian-style evening gown, sits in an oversized rocking-chair which mysteriously rocks of its own accord, and delivers a mesmeric, circular monologue about the end of a life. As she delivers the last line, Dwan's head droops to one side – the end has come. Compared to the previous two plays, Rockaby is almost soothing, although Dwan's performance is no less compelling. Dominated by the darkness, this is an unsettlingly memorable and brilliantly executed hour of theatre.

• Not I, Footfalls, Rockaby is at the Royal Court Theatre until 18 January. It then transfers to the Duchess Theatre 3-15 February