Alex does not voice the cruellest words he ever spoke. We don’t actually hear the dreadful phrase he utters to his father-in-law. But we can imagine it. Playwright Simon Stephens is too subtle a craftsman to allow his central character to blurt it out; instead he pushes us carefully and confidently to the point where we need only fill in the dots.

The theme of the playwright, whose Pornography was named best play in the recent Critics’ Awards for Theatre in Scotland, is the impulse to believe in God and the more awesome prospect – as he would have it – that no God exists. The story told by Alex in this exquisitely realised 30-minute show from London’s Bush Theatre is an everyday story of young love, fatherhood and family bonding which Stephens booby-traps with a shockingly meaningless tragedy. Can the God we thank for life’s unfathomable beauty also be responsible for its inexplicable cruelty?

As theological arguments go, Stephens is not the first to ask the question, but he weaves it into the flow of his narrative so subtly – a phrase here, a fragment there – that you almost don’t notice when the theme emerges. Much credit for this must go to actor Andrew Scott who, under the direction of George Perrin, gives a performance with an authority you’d want to call dazzling were it not so undemonstrative. Wearing workaday T-shirt and jeans, he brings a beguiling sense of spontaneity to the script, as if he too were hearing it newly minted, finding pockets of humour and bucket-loads of charm in his conversational delivery.

He draws us compellingly into his breathtaking romance, the unexpected affection that grows for his oddball father-in-law in the South of France and the unconditional love for his daughter. All of which makes his change of fortune so much more brutal and the big questions about God that much more vivid.

Traverse, 228 1404, until 16 Aug, times vary, £10–£11 (£5–£7).