The work begins long before the curtain rises

Ask most theatregoers what a stage manager does and you will get a vague answer about clipboards and torches. Ask someone who has spent twenty years doing it, and you get something far more interesting: a portrait of a job built almost entirely on anticipation.

"People think the drama is on stage," she tells me, sitting in the back of an empty auditorium with a mug of tea going cold beside her. "Actually, the drama is everything that nearly went wrong and didn't. If I've done my job properly, nobody notices me at all. That's the strange pride of it."

We meet during a technical week, that peculiar limbo between rehearsal room and first preview, when the show is rehearsed and the building is not yet ready to host it. Her company has three days to stitch the two together.

The rehearsal report: small print, big consequences

Every evening after rehearsals finish, a document goes out. It is not glamorous. It lists who was called, who was absent, which props were used, which ones broke, what the director asked for and by when. It lands in inboxes across the building before anyone has had dinner.

"It sounds bureaucratic, and I suppose it is," she says. "But it's the single most useful thing I produce. The wardrobe team reads it and knows a button popped on a jacket in scene four. The lighting team reads it and knows the director wants a slightly warmer wash for the second half. Nobody has to be told twice, and nobody has to guess."

She is firm about timing. A report sent at midnight is a report read at eight the next morning. A report sent at eight the next morning is a crisis.

• Be specific. "Tidy the props table" means nothing; "the teacup needs to be stage left of the script, always" means something.
• Name the person. Tasks sent to "everyone" are completed by no one.
• Flag risks early. A wobbly flat on Tuesday is a collapsed flat by Friday.
• Keep the tone neutral. Reports are records, not opinions.

Cue calls and the art of the quiet countdown

The most visible part of the job happens in the dark. Standing at the desk, headset on, she calls every cue in the show, usually with a short warning followed by the word itself.

"Standby lighting cue forty-two. Lighting cue forty-two... go."

The rhythm matters more than the words. Call too early and the operator jumps; too late and the moment sags. Deputies learn it the way musicians learn tempo, by doing it badly for a while and then, gradually, not.

"I tell new assistants that you're not giving orders, you're keeping time for a group of people who can't see each other," she says. "It's closer to conducting than managing. And you never, ever shout. The moment you raise your voice, everyone on that headset thinks something catastrophic has happened."

She admits to a private superstition: she never says the words "good luck" before a first preview. "It's not that I believe in curses. It's that the cast believe in them, and my job is to remove obstacles, not add them."

When things go wrong, calm beats perfect

Something always goes wrong. A quick change runs long. A radio mic dies mid-ballad. A piece of scenery refuses to fly.

"The instinct is to fix it loudly," she says. "That's almost always the wrong move. What you want is a small, calm decision made fast and communicated to the right two people. Nothing else."

Her rule for a crisis is blunt: protect the actor, protect the audience's experience, then fix the machinery. In that order.

• Give the performer something to do rather than something to worry about.
• Tell only the departments that need to act — the rest can wait thirty seconds.
• Write it down immediately afterwards, while the details are still accurate.
• Debrief the next day, never in the interval.

The rituals that hold a building together

Calls mark the shape of an evening: the half, the quarter, the five, the beginners. To an outsider these are announcements. To a company they are a kind of reassurance, a heartbeat.

"The five-minute call is my favourite," she says. "Everybody's in costume, makeup's done, the front of house staff are opening the doors, and for about ninety seconds the whole building is quiet and ready. That's the moment. That's why I still do it."

She is careful about what she asks of a company. Check the props table before you leave. Sign in, even when you're early. Say if you're struggling with a quick change, because a problem shared on Tuesday is a problem solved by Thursday.

"Perfection isn't the target," she adds. "A perfect show doesn't exist. What exists is a show where everyone trusts the person next to them, and where the person calling the cues has thought about the worst case so thoroughly that nobody else has to."

Then the beginners are called, the house lights dip, and she takes a breath, leans into the microphone and starts counting the show down. The audience settles. Nobody, quite rightly, notices a thing.