For 32 years, Helen Wood’s family didn’t talk about Philip. He was her much-loved brother, her childhood hero and mentor; but in his twenties depression overtook him, and one day he ended his own life. It was only much later, after her mother died, that her dad ended the code of silence, and set Wood on the path to learning more about this real-life personal tragedy. In this poignant but surprisingly humorous show, she chronicles her journey of discovery – and speaks, with searing honesty, about her own search for closure.

But she doesn’t face that challenge alone. Joining her on stage is actor Gregor Hunt, who plays assorted key characters from Wood’s story: her grief counsellor, a clerk from the coroner’s office, her father, and – most strikingly of all – Philip himself. Within the world of the play, Wood is Hunt’s scriptwriter and director, and she jumps in and out of her scenes with him to offer witty asides and commentary. (In the real world, Wood and Hunt are both credited as writers, while the restrained but potent direction is provided by Derek Bond.)

The setup proves a clever gambit, which the pair develop in a variety of ways and always to great effect. When Wood is forced to confront unanswerable questions, she poses them to Hunt – who, with no scripted response to deliver, is agonisingly uncertain of what he should say. When it begins to get too heavy for her, as well as for us, she instructs Hunt to return as her therapist Richard… yet by controlling the script, we know she’s controlling her own self-doubt.

Most electrifying of all is when Hunt plays Philip – especially in his harrowing, imagined, final meeting with Wood. We get the sense of a man who was happiest pushing onwards, driven by excitement but tragically unable to summon resilience when his fortunes changed. There are sad truths here too about how the closest of companions can neglect each other, and how important it is to make time to stay connected with the people we care about. It’s all summarised by one simple but devastating question, which Wood asks again and again: did anyone ask Philip how he was?

Yet for all that sadness, this is at times a very funny show. Hunt’s rendition of the coroner’s report is marvellously entertaining, channelling an Elizabethan courtier to reflect its archaic legal tone, while a physical visualisation of a long series of emails is a comic highlight too. The set, meanwhile, is sparing and stylish: props emerge from the suitcases which surround the stage, while the growing bundle of documents Wood has unearthed is gradually spread out on a whiteboard behind her.

It feels important to ask what Philip would think about this show – whether he’d be comfortable seeing his life deconstructed, hearing extracts from his letters read aloud. But that’s a judgement I’m happy to leave to Wood; she knew him, and I did not. What I do know is that this is a beautifully constructed, utterly engaging play, powered in equal amounts by Wood’s insightful candour and by Hunt’s flawless characterisation. I’ll be talking about it for a long time to come.