ONE was the most glamorous monarch of her age, a devout young Catholic woman who loved music, poetry and art. The other was a pivotal figure in the European Reformation, a dour Protestant revolutionary who advocated – nay demanded – an austere existence based on the gospels.

Mary, Queen of Scots and John Knox continue to loom large over the Scottish imagination, representing two opposing sides of the Caledonian psyche. Now a new play at the Royal Lyceum in Edinburgh seeks to explore their relationship and the profound influence each had upon the other, amid one of the defining and most tumultuous periods in our nation’s history.

Focusing the action around Mary’s arrival from France at the age of 19, and the four meetings she held with Knox, then in his late 40s, between 1561 and 1563, Glory on Earth examines how these two powerful, sometimes misunderstood figures battled for the heart and soul of Scotland.

Rona Morison takes the role of Mary and Jamie Sives plays Knox in Linda McLean’s poetic reimagining, which incorporates live music performed by the cast and is directed by the Lyceum’s artistic director, David Greig.

In concentrating on her relationship with Knox, the play represents a departure from recent retellings of Mary’s story, which have focused on her fatal dance with her English cousin, Elizabeth I. Indeed, a £180 million Hollywood biopic starring Saoirse Ronan, which starts filming in Edinburgh this summer, will centre on the two queens, echoing the 1971 film starring Vanessa Redgrave and Glenda Jackson, and Scots playwright Liz Lochhead’s celebrated 1987 play Mary Queen of Scots Got Her Head Chopped Off.

But McLean, who devoted a year to research, believes Mary’s early years in Scotland also deserve attention since in her view they had such a significant impact upon the monarch’s tragic fate.

“One of the big things for me was not making it about Elizabeth,” says the award-winning playwright, whose works, which include Any Given Day, Strangers, Babies and Every Five Minutes, have been performed across Europe and North America.

“Everybody knows that story. What fascinated me much more was how the first two years of Mary’s reign set up her downfall to come. I think 1561 to 1563 were her most important years. I came to understand her later decisions – the marriages to Darnley and Bothwell, going to Elizabeth for help – through those first two years. That’s what I hope people will come to understand when they see the play.”

We’re talking in hushed tones in St Giles Cathedral on Edinburgh’s Royal Mile, where Knox was minister for 13 years until his death in 1572. It’s a pivotal place for anyone who wants to understand the man and his mission. An ornate and colourful stained-glass window depicts Knox’s ministry, while a bronze statue, complete with long beard, stands nobly in one of the aisles. “Knox would have absolutely hated both of those,” McLean, a Glaswegian, says. “It’s so ironic – they represent everything he stood against.”

The Scotland that Mary arrived into in 1561 was a country in the throes of social, religious and diplomatic change; and it was in turmoil. Protestant nobles were in charge, allied with England, the auld enemy, rather than the France of the Auld Alliance, from where Mary had come following the unexpected death of her young husband, Francis II.

The reformation was sweeping violently across Europe and much to Knox’s annoyance it was agreed that the new Scottish monarch should be allowed to practise her religion privately, as long as she abided by Scotland’s Protestant public settlement. Meanwhile, Mary’s claim to the English throne meant many Catholics there were relying on her to restore the Church of Rome in both kingdoms. Then there was her status; as a young widowed queen, Mary – in common with Elizabeth – was under pressure to marry and produce an heir.

Knox, meanwhile, was fixated on Mary – “that wicked woman" – viewing her not only as a danger to Scotland’s newly established Protestantism, but, because of her sex, unfit to rule; he infamously wrote in 1558 of “the monstrous regiment of women”.

And while his account of their meetings are well documented in his five-volume History of the Reformation, few attempts have been made to bring them to life from Mary’s perspective. Until now.

“Knox writes from his own perspective, obviously, and his narrative is very self-serving,” McLean explains. “As a woman, the thing that really stands out is how he infers what Mary was thinking and feeling, that a certain response was because she was angry or undereducated or something else. And he was so openly insulting to her. I found that extraordinary and I wanted to do something about it, to give Mary a voice.”

McLean devoured caches of letters, now held in St Petersburg, which were written by Mary during her 19 years in captivity.

“There were endless letters asking for help, for her release, for her servants who had been sacked to be looked after,” she says. “And eventually I did start to develop a picture of who she was. The power balance between Mary and Knox became the story. But the starting point for me was trying to get into the head of this young girl, a 19-year-old who is coming back to a Scotland that no longer really belongs to her, who probably fears for her life.

“All of a sudden one day I just heard this young woman’s voice and from then on I never wavered.”

Knox, meanwhile, first came to the playwright in a dream, beckoning her towards him with his finger. “I was a bit alarmed by it,” she says, smiling, as we examine the statue in St Giles, erected in the 19th century. “But the next morning I got up and read his favourite gospel – John – and started to really appreciate the poetry. And bit by bit that terror of putting words in his mouth left me.

“I came to have a real respect for him. He was absolutely devoted to the gospels and God. In fact, I long for him to rise up now and point people in a direction that is not so self-serving and motivated by money, that encourages deeper thinking about what it is to be in the world.”

McLean admits her play is likely to cause some controversy, especially since it inevitably touches on very modern themes, including gender politics and sectarianism. “I take a very strong view about what it was to be a young woman at that time,” she says. “We’re not be able to avoid questions around whether John Knox was a misogynist. And another of my starting points was around how we in Scotland, small nation that we are, have managed to remain in so many places so sectarian.”

In the Lyceum’s rehearsal rooms in Edinburgh, just across the street from the main theatre, David Greig is watching intently as the cast rehearse a scene where Mary and her "Marys" – the queen’s ladies in waiting, all of whom were called Mary – arrive in Leith amid what the history books told us was “a good haar”. It’s a beautiful, powerful moment, imbued with music, sound and movement, seen entirely through the eyes of the young monarch.

Later, we watch as Morison and Sives, last seen together in the National Theatre of Scotland’s electric staging of Rona Munro’s James plays, run through a one-to-one encounter between Mary and Knox. The tension is palpable as this monarch and commoner, younger woman and older man, Catholic and Protestant, confront each other. As an audience member, your allegiances may change in unexpected ways; don’t presume either Mary or Knox to embody in this piece the caricatures foisted upon them by history.

The play couldn’t have come at a more relevant time, of course, as Scotland again finds itself divided, facing big, unwieldy questions about its relationships with England, Europe and the world.

Greig is an accomplished playwright, who has adapted Charlie and the Chocolate Factory for the West End and Broadway, and is behind modern classics such as Dunsinane, The Events and Midsummer.

The playwright, who is entering his second season as artistic director at the Lyceum, is alive to these contemporary parallels.

“There’s a sense at the moment that we must reflect upon the condition of being human together, and this play is such a good example of that,” he explains. “It couldn’t be more specifically about Mary and John Knox. But through that Linda [McLean] talks about so many things: patriarchy, global politics and Scotland’s position within that, God, where authority lies, the problems when there is division in a kingdom."

And he believes the play offers an opportunity for us to reassess Knox and question notions of national psychology.

“There’s not a Scot alive for whom Knox isn’t a pretty constant traveller and companion," he says. "I always joke that I have a little ‘JK’ in my head, who pops up, jabbing a finger and says, ‘You’re not doing enough work. Why are you having a drink? Why are you having fun?’ He is very much in our imagination. But also we like him. There is the line in the play where he says, ‘I am a citizen, nothing more, nothing less.’ He’s about reading and education, practicality, being humble, hard-working.

“Mary is about joy, poetry and love of music, but there’s a few steely lines where you realise for her it’s also about shallowness, divine authority and monarchy.

“Linda first spotted the possibilities in this story, but I believe the psyche of Scotland was born in that big bang moment. Modernity in Scotland comes out of it. It’s the hinge the history turns on.”

Greig, who was born in Edinburgh and lives in Fife, says he’s enjoying the challenge of directing his first play at the Lyceum, particularly because he has been a long-time admirer of McLean’s work.

“It’s very exciting to be the first person to direct Glory on Earth and I wouldn’t have given it to someone else,” he says. “It’s been a lovely process. Linda has written a play there’s no right way to do, a text full of poetry, drama, colour and life. It needs a commitment to a type of creation, a vision, and that has been the fun and the challenge, finding a way to stage a play like this – there are 100 ways you could do it.”

Greig was a prominent supporter of independence during the 2014 referendum. He says unsettled questions about the future of Scotland filled his mind as he commissioned work and created the theatre's forthcoming programme, particularly since Brexit added another complex layer of political, social and constitutional uncertainty. He believes art plays an increasingly important part in how we process the turmoil around us.

“If there was ever a time you would want to be programming a public space, it is now,” says Greig. “In 20 years people will be saying, ‘I wonder what they were programming during that extraordinary time.' I really want our programme to answer that.

“When this play was commissioned I knew we were in a period between two independence referendums. We’d left one behind and I imagined then – I still think I’m right – that in three, four, five years’ time there will be another. Over the next few years I want to build a body of work that reflects on Scotland and where we are now.

“I don’t know how all this [Brexit, independence] will play out, but I doubt there will be a more interesting two or three-year period in this country’s history. I want us to play a part in shaping that.

“Theatre forces you to experience not just the shared humanity of the characters on the stage and all their stories and differences, but you can’t help encounter the shared humanity of being in an audience and sharing their reactions.

“There will be art made that will directly reflect this time. But for me, it’s more that we’ve never needed art more.”

Glory on Earth is at The Lyceum in Edinburgh from tonight until June 10.