Being upstaged by a co-star is surely every actor's biggest fear, but how do you avoid being eclipsed by several tonnes of churning metal?
That's the dilemma faced by Louise Calf, now appearing in Mike Kenny's Olivier Award winning stage adaptation of Edith Nesbit's cherished novel The Railway Children.
She shares the specially constructed stage behind King's Cross Station with a working steam engine, which chugs into view for the climactic scene - one of British cinema's most iconic moments.
But there's no hint of cattiness in her voice, only awe, as she discusses the show-stealing vintage locomotive, on loan from York's National Railway Museum.
"It's a beautiful piece of machinery, which really adds to the show, and we're so lucky to have it here," says the actress, who grew up in west London, living in East Sheen, studying at Richmond College in Twickenham and working at libraries across Richmond.
"Sometimes we'll see a man of a certain age on his own in the front row at a matinée and wonder if he's a train enthusiast, but I think the appeal is universal. It's ridiculously exciting, especially for the younger members of the audience, when the train comes on."
There are drawbacks of course to starring alongside moving machinery, which can be as temperamental as the biggest showbiz diva.
One preview was held up for three minutes when the train refused to come on stage, not due to a hissy fit but because someone had accidentally walked in front of the vehicle backstage.
As Louise explains, the safety measures are incredibly tight, which meant the train was automatically disabled when the alarm was triggered - somewhat ironic given the nature of the play's most famous scene.
Louise plays the youngest sibling Phyllis in the drama about three children who move from London to rural Yorkshire, where they befriend the local railway porter as they try to solve the mysterious disappearance of their father.
It is the first time she has appeared alongside her real-life mother-in-law Caroline Harker, who has been in her life since she was eight. But she says their on-stage relationship is very different to that in reality.
"We're very close but I'm nothing like Phyllis and Caroline is much more fun than the mother in The Railway Children," explains Louise, who was an only child for many years but now has four half-sisters. "Phyllis is the youngest sibling and there's something liberating about that because you don't have to take responsibility, which is why she has no filter."
The Railway Children belongs to a bygone era and Louise believes that it key to its enduring appeal.
"It's very uncynical and I think we miss that today. There's something very pure and wholesome about it," she says.
"I think the child stays within us and we miss that lost innocence, so there's probably an element of nostalgic yearning for adults watching."
Tickets for The Railway Children cost £25-£49.50, with £1 from every seat going towards the Railway Children Charity to help homeless and runaway children across the world. They are available at www.railwaychildrenlondon.com.
Children can apply to join the cast of The Railway Children by auditioning on March 7 and 14 at a central London venue to be confirmed. They must be aged nine to 15 and no taller than 5ft 3ins for girls or 5ft 6ins for boys. To register for an audition, email firstname.lastname@example.org.