It is 14 July 2017. Donald Trump is guest of honour at the annual Bastille Day celebrations in Paris – a double whammy that year, marking the centenary of America’s entry into the first world war. Emmanuel Macron and the French weren’t stinting – there was pomp, ceremony and lavish military displays, not to mention handshakes between the two new presidents. Handshakes that went on and on … and on, like some bizarre courtship ritual, simultaneously friendly and mildly aggressive.

But as they primped and preened and smirked and backslapped, my eyes were drawn not to the men but to the two women standing, somewhat awkwardly, either side of them trying to smile. The wives. Brigitte Macron, the former schoolteacher who, it was noted relentlessly at the time, is 25 years older than her husband, and Melania Trump, the ex-model from Slovenia who, it is much less noted, is 24 years younger than her husband. Brigitte, it was widely reported, was the rock of strength with whose support, encouragement and, indeed, rumoured coaching, Macron had built his movement La République en Marche, beating the far right Marine Le Pen. Melania, it was generally gossiped, just wanted to run for the hills.

Embarrassed or exhilarated? Brigitte Macron and Melania Trump stand either side of the French and US presidents. Photograph: Christophe Archambault/Pool/EPA

“What do they make of all this, really?” I wondered, as I watched the women glance and smile at one another, something polite but strained in their interactions. Were they embarrassed? Exhilarated? Bored? These silent women, whose only means of communicating at such events is generally what or who they’re wearing – what do they say to one another when the doors close and the cameras depart? And what’s it like to be in such close proximity to power but not – in the direct sense at least – to have power yourself?

These questions were the seeds of my play Two Ladies, soon to open at the Bridge theatre in London, starring Zoë Wanamaker and Zrinka Cvitešić and directed by Nicholas Hytner. The play presents an alternative reality involving a heightened global crisis. The two ladies in question are fictional characters, but admittedly share similarities with certain real-life ones. Wanamaker plays the English wife of a fictional French president, while Cvitešić plays the Croatian wife of a fictional American one. Both bring their considerable theatrical abilities and cultural backgrounds to roles that present two first ladies in a high-stakes situation.

High-stakes situation … Zrinka Cvitešić and Zoë Wanamaker in Two Ladies. Photograph: Helen Maybanks

Playwrights tend to look for gaps. The best stories are often found in that space where the real world meets the unruly underworld of our imaginations. Watching Brigitte and Melania that day, I began thinking of the women of Greek mythology: Helen of Troy, whose famed beauty supposedly sparked the Trojan war; and Iphigenia, sacrificed at the hands of her father so the winds could change and the Greeks could sail for Troy. These mythic women were so often the catalysts for the action of Homeric epic poetry, but banished to the sidelines of the action itself. (Except for Penelope in The Odyssey who, thrillingly, gets to wait.)

Had you asked me three years ago if I had a particularly avid interest in writing about first ladies, I might have laughed. In this era of third-wave feminism and #MeToo, when Angela Merkel and Jacinda Ardern and, yes, alright, Theresa May have proven that women can and do make it to the top jobs in politics, why should any of us care about the wives? What even is the point of a presidential spouse, other than to be married to the president? And anyway, hasn’t the role changed with the times? In Ireland, where I’m from, our Taoiseach Leo Varadkar has a boyfriend, Matthew Barrett. In the UK, Carrie Symonds has become Downing Street’s “first girlfriend”.

Balance of power … Angela Merkel amid a throng of male world leaders at the G7 summit in Biarritz. Photograph: Ian Langsdon/EPA

Roles are evolving, things are moving on … but then up pop photographs like those from the G7 summit in August, where Angela Merkel is the only woman amid a throng of male world leaders. Or last June’s G20, where presidential spouses are lined up like expensively dressed schoolchildren and Philip May is the only man. And we realise that actually, shockingly, not much has changed at all. The role of presidential partner is still primarily a female one, and the balance of world power is overwhelmingly in the hands of men.

But what of the role itself? Lady Bird Johnson famously described the first lady as “an unpaid public servant elected by one person, her husband”. In the US, where her popularity plays a role in his, the president’s spouse tends to serve as part of the administration, with her own offices and her own staff. She hosts state dinners and has official duties. But in other countries, the position is far less well defined. In France, for instance, Macron introduced a “transparency charter” to clarify the role of presidential spouse – and the amount of public money being spent on her. But his reported intention to give his wife a budget, salary and official title was met with derision, outrage and a petition of protest signed by almost 300,000 people. He backed away. The French were adamant they did not want an official première dame.

Lady Bird and Lyndon Johnson in 1955. Photograph: AP

This reveals a larger issue: the suspicion with which we treat a presidential spouse if they appear to be angling for more power than deemed appropriate. Having access to those in power means being able to exert influence. Exerting influence when you haven’t been elected is dangerous to a democracy. And who is better placed to wield undue influence than the person sharing the president’s bed?

But is proximity to power a red herring? What about the cost? Michelle Obama and Hillary Clinton gave up highly accomplished, professional careers to take on the unpaid role of first lady, with all the scrutiny it entails. Each has talked about the “privilege” and “honour” of serving their country. But wasn’t it also a sacrifice? And a painful one at that? Would they tell us if it was? And once their husbands were elected, what choice did they really have? How can we ever know the true personal cost to these women of supporting their husbands politically, when all we ever really see is what their spin doctors, speech writers and carefully crafted memoirs want us to?

Which brings us back to mythology. I’m aware it’s a stretch to compare Melania Trump to Helen of Troy or Cherie Blair to Iphigenia, but in a general sense, I feel there is some truth in it. It took the tragedians of fifth-century BC Athens to give voice to the women of Greek mythology. Without sounding grandiose, or worse absurd, I wondered if it was worth exploring something similar with first ladies. After all, is there not something mythic about these women whom we watch on the world stage but never truly know? And if they did get to speak, might they be able to bring us a new kind of political – and personal – story, that resonates with our times?