Constellations by Nick Payne at Cambridge Arts Theatre until Saturday, June 20. Review by ANGELA SINGER.

Clever theatre can be like jazz. You might need to be a performer to fully appreciate the difficulty of what the performers are doing.

Certainly the performances in Constellations are stellar, beguiling and heart-wrenching.

The play, which opened at The Royal Court in 2012, rests on the idea that somewhere, in a set of parallel universes, every outcome of every situation is happening. In your consciousness you make one decision but out there, in the ether, you do it differently and there is another result.

We see a love story unfold, a relationship develop in all possible ways. We see Marianne (Louise Brealey) and Roland (Joe Armstrong) meeting at a barbecue and either getting together or going their separate ways.

We see them marrying or not marrying. We see one of them struck down by a fatal illness or see them making a complete recovery.

On a dark stage filled with brightly lit balloons evoking the heavens, this is an hour’s performance with no interval, because it is crucial not to break the thread.

The little scenes, brief exchanges, are repeated, two, three and four times. Each take has a line changed or the tone altered, so retrospectively, the audience has built an understanding of what is going on. The changes are funny. At first it’s bellylaughs. Later it’s tragic and gripping.

This is a two-hander with repeated lines. The story unfolds out of sequence, you only really understand the speeches right at the end. It’s a challenging showcase for the actors. Joe Armstrong gives a natural, heart-warming performance as an uncomplicated young man who finally faces an impossible situation. Louise Brealey gives her character a haunting strength and frailty.

An incisive piece of theatre.