Tim Crouch's My Arm was one of the highlights of the 2003 fringe and an international success. He's done it again with An Oak Tree, in which he experiments with the theatrical medium while unfolding a haunting story.
In each performance of this play the Father is played by an actor who has never seen or read a word of the play. He is instructed by the Hypnotist, sometimes audibly and sometimes through a set of headphones. No improvisation is involved on the part of the Father, they simply do what they are told. This is not a gimmick, it relates directly to the story, though I don't want to give too much away.
The best way to experience any play is through performance, and this is especially true of An Oak Tree. I found the play so fascinating though, that I bought a copy of the text afterwards so that I could re-read and come to understand the play a bit better. Crouch is a brilliant writer who brings out all the complexities of his themes through his techniques.