Theatre503 and Sheer Drop Theatre’s Valhalla has a lot going for it. Not only did it storm past over 1600 other submissions to become the joint winner of the Theatre503 Playwriting Award, it is in the hands of acclaimed director Jo McInnes who, despite being busy with rehearsing, preparing and – oh – running a celebrated show, managed to spare a few moments to tell me more.

McInnes is no stranger to working with prestigious theatres – the Royal Court and the National, to name a couple. Unlike these famous haunts, Theatre503 might not show loud, proud and money-pumped productions, but it is a fringe favourite, hosting ground-breaking and unique theatre. It seems Valhalla more than lives up to the well-received past work of Theatre503, including last year’s A Handful of Stars that won an Off West End award, and is already being well-received by the press. Theatre503 is also a hub for new writing, which McInnes thinks is the “most exciting area of theatre”.

Written by London-based playwright Paul Murphy, quite incredibly as his first full-length play, Valhalla “sees a couple trying to discover a new medical treatment who escape to an isolated research facility, and the impact the ups and downs of their work have on their relationship”, says McInnes. “This doesn’t do justice to the layers of the story, of course – within this it explores themes of Norse mythology; the role of science, magic, nature and belief; genetics and epigenetics; gender politics; the limits of human love; morality and its impact on personal relationships.”

“Learning about epigenetics blew my mind”, says McInnes. Now one of the hottest topics in biology, epigenetics is hard not to find fascinating: your DNA, it turns out, is not a bound, rigid set of commands like a book, but is in fact as editable as Wikipedia. Though your genes themselves don’t change, chemical modifications mean that whether or not they are expressed does – in other words, their instructions can be ignored or listened to. Mind-blowingly, this can change in your lifetime and even be inherited. McInnes is mesmerised by “the impact our DNA has on our behaviour and our behaviour and experiences have on DNA, and that this is a dialogue not a one-way street. Epigenetics shows that our genes adapt due to experiences we have or our parents, grandparents, great-grandparents had.”

A play featuring both tough science and a ponder over the nature of love? Quite a lot going on in Valhalla, then. But McInnes and set designer Katie Lias have managed to incorporate these themes into the set: “Instead of a naturalistic set, we have a white room which could be any room, anywhere really, inspired by images of interrogation rooms, science laboratories, and Scandinavian and Icelandic design. We wanted the space to be clean and direct, forensic – to act like a microscope on the two characters of Man and Woman. Katie Lias has done a brilliant job, along with the amazing Nigel Edwards (lighting) and Becky Smith (sound), to create this intense space.”

Rehearsal “was about finding the tension between the two people in space, maintaining that tension, so that every word or look or gesture has meaning”. The draw of theatre, of course, is that it offers a live experience, and McInnes tries to nurture that in rehearsal. In this way, the tone of the tension onstage may be different from night to night. “I believe strongly that you don’t ‘solve’ the play in rehearsals and then just present it – each performance has to life and breath in its own way and if you see the show more than once you will see the play done two different ways, because the process doesn’t just end on the first night.”

Valhalla is a tough one to miss out on. It “really is unique – a thriller/sci-fi/love story which is full of ideas but ultimately very human, very affecting because we recognise ourselves in these two people. It shows both the best and worst of humanity alongside each other, that there is actually a very thin line between these two extremes.” If nothing else, Valhalla certainly promises to be thought-provoking. But from what McInnes has said to me, and the wave of raving reviews following its opening night, I’m sure a deep delve into ideas is far from all the riches Valhalla has to offer.

Valhalla is playing Theatre503 until 24 October. For more information and tickets, see the Theatre503.