An Oak Tree by Tim Crouch is an exploration of theatre, asking the audience to accept everything. It’s an exploration because the other actor in the production has only met the writer, director, other actor Crouch in the last hour. They have never seen or read the play beforehand. Therefore they learn and discover everything afresh alongside the audience.

Crouch uses a different second actor every show, so no two will be the same. Whether they are male or female, they play the role of Father; this time the character Father was played by Maggie Service. This element is introduced beautifully by them asking “what am I being?” and a full physical description of Father is given.

An Oak Tree breaks the forth wall and directly addresses the audience but asks nothing from them. The play has an hypnotic air about it, like watching a live experiment or surgery, with the audience concentrating to see what they know will happen, then happen. Crouch tells the actor where to stand what to say, or hands them a piece of script on a clipboard. Service has headphones in and music plays whilst he speaks to the actor privately, yet the actor does little during this point – I can only guess he was giving her back story or motivation to catch up on, so the next part of the script has context.

Crouch is a very skilled actor amongst his other attributes. His calmness and confidence relaxes the audience and the other actor he’s working with. Apart from him repeatedly letting the Service know that “it’ll be ok”, he radiates a quality through which the audience trust him too. He has the ability to instantly go in and out of character quicker than you think possible, but extremely clearly. His character traits whilst playing the Hypnotist are extraordinarily detailed: he gulps and mixes up words with such intricacy that you question whether it is the microphone breaking and missing gulps of sound? But no, it is his purposeful misdirection of words.

The moment that stands out for me is when the two actors sit back to back, whilst ‘Father’ reads out a mediation script and Dawn (the character Crouch is playing at that point) wails her distraught screams over it. It is distressing and the juxtaposition of it is powerful. The set is minimal and all exposed, while Crouch works the sound himself from a little table at the back of the stage, and has all the actor’s scripts ready on the same table. An Oak Tree deconstructs theatre to see the ingredients involved, so it is fitting that the backstage elements are exposed too.

The beauty with Service’s lines is that everyone, including her, is hearing them for the first time. Most of the direction comes from Crouch saying “you say”, and then giving the other character’s line for them to repeat, before introducing his own line with “I say”. It is a very simple process of “You Say, I Say”, but it made me look at theatre in a way that is bizarre.

The play contains lots of elements of hypnotising, with Crouch repeatedly telling the actor that “you’re doing really well”, and asking the audience to “nod your head if you understand”. Yet at the same time, halfway through Crouch asks Service to sit, followed by a scripted chat about how she thinks it’s going. The production exposes so many elements of theatre: the actor’s nerves and eagerness to impress, and the audience’s reality of trying to believe in something that they know is not real. It un-hypnotises the audience about what theatre actually is, but the wonderful thing is it is still powerful.

An Oak Tree is playing at the National Theatre’s Temporary Theatre until 15 July. For more information and tickets see the National Theatre website.