On Saturday night, I took myself out to see Misterman at the National Theatre. It has its last show today, so I’m afraid you missed it. Otherwise, I would urge you to go see it.

Misterman is a one-act, one-man play by Enda Walsh, whose work includes Disco Pigs, Penelope and the book for the musical version of the movie Once, currently playing to rave reviews on Broadway. The big draw for me however was that the one-man in this play was Cillian Murphy.

If you don’t know who Cillian Murphy is, then you’ve missed some wicked movie experiences, as he’s in Batman Begins, Inception, Sunshine and Breakfast on Pluto, amongst others. He is a brilliant actor – and let’s be honest, rather easy on the eye. I’ve seen him once before on stage as my friend Beth took me to see Love Songs in 2006, which I believe was the first play I saw in London! Love Songs was fine, but nothing like this.

Lyttelton Theatre is a massive, massive space. I’d say it would easily take a cast of a hundred. Instead we had one Mr Murphy taking on this massive space in two levels as Thomas Magill, a young man who at first comes across as a fairly innocent religious obsessive, but shows increasing signs of madness, delusions and violence as the play progresses. Thomas is locked into an industrial space where he keeps replaying one day of his life, partially by reliving recordings of people, and at other times by acting out every other character he comes across. At points it’s very funny, especially at first when he fights a tape recorder that keeps playing a Doris Day song, and doesn’t stop when unplugged, or after he pulls out and throws away the batteries. He stomps on them with determination and even takes out the tape. Then we watch him prepare for his routine, going through the day’s events. At first we really like Thomas. He’s a religious fanatic who writes down what he considers to be the sins of people he meet, and has a grand dream of bringing the local population to the lord. He seems a bit off, but harmless. As we dig deeper into the day, and how Thomas responds to his surroundings, the play gets more and more disturbing before culminating in a moment that is so disturbing I am reluctant to describe it.

A lesser actor could not make it work. Murphy’s energy and presence carries the piece, with him hurling items around, running and jumping onto props, and carrying himself completely differently for each character he, as Thomas, embodies. Thomas is what we’d call an unreliable narrator, as we only see the events of the day from his point of view. It’s a powerful and gripping performance that I will never forget.

The play left me with so many questions. Where is Thomas? What happened in his past to make him the person he is? What happens after the end of the play? How long has he been replaying this one day? I have my theories, none of which would make sense without describing the latter half of the play, and I’ve decided to spare you. Even with just one person present on stage (everyone else are acted out by Thomas or appear as audio recordings), it is one of the most harrowing theatre experiences I have ever had. I left the theatre stunned, walked through Waterloo station with a lump in my throat, and when I got home I grabbed both guinea pigs for a cuddle. I was a bit shell-shocked.

It’s a performance I will remember for the rest of my life.