Back in 1973, the BBC screened an epic documentary series called The Ascent of Man – an optimistic, even triumphant, celebration of the progress of humankind. Its host was Jacob Bronowski, a mathematician by training and a popular scientific historian. But Bronowski had a secret; there was a locked room in his house, which even his wife was forbidden to enter. This intriguing new play, featuring fictionalised characters but based on fact, follows Bronowski's grandson as he opens the locked office and finally uncovers the truth.

Richard Delaney is quietly commanding as Bronowski, anchoring the performance with his reassuring, timelessly educated tones. And we need that anchor, because playwright David Byrne's script has mind-blowing scope – including fleeting scenes from prehistory, continuing through the Second World War, into the 1970s and on to the present day. It covers a lot of intellectual ground too: there's a loose theme around whether we should be optimists or pessimists in the face of scientific progress, but this polyglot production draws inspiration from mathematics, anthropology, ethics and even religion.

In the modern-day scenes that frame the play, a boy-meets-girl story's playing out: a humorous tale involving Tinder, a shy first date and a little bit too much alcohol. But the more touching love story surrounds Bronowski and his wife Rita, who survived him by 36 years and yet – if the play's to be believed – never tried to learn what he'd been hiding. The story of how they met is sweet and quirky, and they get the honour of ending the play too, an ending that's as inspiring as it is beautiful.

Bronowski's secret, when it's revealed, is genuinely troubling; not because it's something too horrible to contemplate, but because of the ethical and moral dilemma it evokes. It ties neatly into the play's big debate, about whether the march of progress detailed in The Ascent Of Man is really as inevitable as Bronowski's series claimed. Pleasingly, the script reaches no conclusions, posing interesting questions without presuming to lecture us on the answers.

The staging is audacious. Moving bookshelves conjure the locked office, a living room, or a library, while also providing cover for Bronowski to sneak onto the stage and appear – like the ghost he is – in the middle of a scene. Black-and-white footage from The Ascent Of Man is cleverly projected onto a giant chalk-smeared blackboard, lending the whole production a comforting retro feel. And the choreography of the actors' movements is impeccable – which is fortunate, since the risk of being knocked flying by a spinning bookcase at times seems very real.

A little more could be made of the locked room – one moment it's mysterious, the next it's been opened with remarkably little fanfare – and the ending of the modern-day boy-meets-girl story felt a little rushed to me. But overall this is an engrossing and well-paced production, which successfully mixes some rapid-fire humour with slower, more contemplative scenes. Polished, visual and thought-provoking, it's a highlight of this year's Fringe.