Caryl Churchill’s A Number is a play one needs to pay attention to. Bernard (Lex Shrapnel) is meeting with his father, Salter (John Shrapnel). However, we quickly learn Bernard isn’t the only Bernard, with there being several other clones wandering the country. In fact, the Bernard we meet isn’t even the real Bernard; the original supposedly died in a car crash, and Salter has cloned him so he could hold on to his son. As a result Bernard has to ask himself, now feeling robbed of his genetic identity, what is left to define him? And what lies has his father told him?

A Number is a clear product of its time, originally written in 2002 when controversy concerning potential human cloning and various genetic projects was more prevalent than it is now. However, the show has not aged, as the play focuses on identity and on what defines us as an individual; as this is a question that has kept philosophers busy for over two millennia, it is always of existential importance. In particular, in our world of social media and instant connection, the dispute between what we portray on the surface and who we are at an internal level makes the piece feel particularly relevant.

Tom Scutt’s design reflects the piece’s themes well, though never imposingly. From viewing rooms, the action is played out on the other side of a one-way mirror, just as if we are the team of scientists watching this little experiment play out. The whole thing has a voyeuristic feel, with a sense of intrusion, and considering the play revolves around a set of human guinea pigs, it works perfectly. Oh, and the transitions offer a shock that startled quite a few of the audience members around me, and certainly make you consider your own identity

The marketing for A Number is keen to tell you that this two-hander about a father/son relationship is played by real-life father and son, John and Lex Shrapnel. Regardless of what impact that may have had on the performances, both Shrapnels deserve praise: this is a piece that picks apart nuances, both tough and beautiful, in the father/son relationship. Shrapnel Senior excels in the self-hating lies of a man who thought he was doing right, and reality is coming back to haunt him, whilst Shrapnel Junior works the pains and pleasures of the various clones, bringing each to life convincingly and truthfully.

Though running at less than an hour, the piece is crammed with enough intelligence, wit and emotion to leave one completely satisfied, and possibly elated – akin to a shot of adrenaline. A particular delight is the final screen, which – whilst avoiding any spoilers – after tough, existential despair and frayed relationships throughout the rest of the play, ends it on a hopeful message: that we define our lives through living, and not the other way round.

A Number is playing at the Young Vic (The Maria) until 15 August. For more information and tickets, see the Young Vic website. Photo by Johan Persson.