A woman staggers into the Ladies’ Powder Room at the Queen Victoria Building with red eyes. She checks to see if anyone is occupying each of the three stalls before allowing a sob to escape. She washes her face at a basin and uses the mirror to inspect bruises on her shoulder and wrist, lifting her shirt up to examine another on her back. Staring into the mirror, she delivers a haunting, visceral rendition of When I am Laid in Earth, Dido’s Lament from Purcell’s opera Dido and Aeneas, as she counts out pills from a bottle.

It is an excruciatingly intimate scene, in the safe, private and female space of the women’s bathroom – and it all happens inches in front of me, my knee wedged under the basin next to hers.

A deliberate subversion of the “witches, bitches and breeches” roles female opera singers are so often required to play, Clemence Williams’ site-specific pasticcio Chamber Pot Opera tells the story of three strangers whose lives briefly intersect in the Ladies Powder Room. The first woman, sung by Sally Alrich-Smythe, flees to the privacy of a stall as another woman (Jessica Westcott) enters, singing a boisterous L’amour est un oiseau rebelle – Carmen’s famous Habanera – and revelling in a promotion. Engrossed in her phone and agonising over a recent date, Britt Lewis completes the trio – singing a clear-toned, if distracted, Voi che sapete from Mozart’s Marriage of Figaro.

Chamber Pot OperaBritt Lewis, Sally Alrich-Smythe and Jessica Westcott in Chamber Pot Opera

While the opening is dark, the singers – through a series of popular arias, duets and trios – tell a simple yet affecting story of resilience, kindness and camaraderie. Williams playfully reappropriates works from the opera repertoire to bring the focus to the female characters. Lewis sings a feverish Non so piu cosa son, cosa faccio – an aria sung by Cherubino, a breeches role (a male character sung and acted by a female singer) in The Marriage of Figaro lamenting that “every woman makes me tremble”, and an all-female arrangement of Mozart’s trio Soave sia il vento from Così fan Tutte, originally scored for baritone, mezzo and soprano, becomes a kind of purifying anthem.

The performers use the small performance space remarkably inventively. The close proximity of audience and actors gives the performance an emotional tautness that swings from uncomfortably voyeuristic to intoxicatingly uplifting. It’s also an incredibly lean production, relying on the Powder Room itself to provide set and props – the only extravagance is a machine that fills the air with bubbles as Westcott and Lewis sing the ‘Flower Duet’ from Lakmé.

Chamber Pot OperaBritt Lewis, Sally Alrich-Smythe and Jessica Westcott in Chamber Pot Opera

In some ways, though, the production’s greatest strength is also its weakness. The close-quarters venue that gives the piece so much power also means the small audience is squeezed together along a wall, and no matter where the action takes place, someone’s line of vision is impeded. The surtitles (though they are by no means essential for understanding the drama) are projected on a wall above the basins – while the action often takes place on the opposite side of the room. But the sound is surprisingly good – the singers are well balanced in the bathroom acoustic and Darci Gayford does a sterling job accompanying from a keyboard in the corner.

Chamber Pot Opera is an inventive, heartfelt operetta that playfully re-evaluates the roles of women in opera and brings the magic and power of the artform out of the theatre and into the everyday world.

Chamber Pot Opera is in the Queen Victoria Building’s Ladies’ Powder Room until July 22.