Somewhere in every big musical there is a performer in full costume who is hoping not to be needed tonight.
They're called swings. A swing doesn't have a part — they have all of them. On a large show one swing might cover fifteen ensemble tracks: fifteen sets of blocking, fifteen harmony lines, fifteen quick-changes, fifteen places to stand during the number where everyone has to land somewhere exact or the lift comes down wrong. They keep it in a book of charts drawn from above, the stage as a grid, hundreds of little diagrams of who is where on which count. Nobody in the audience will ever see the book. It exists so that at half-hour, when word comes that a flight was delayed or a knee gave out, the swing can read it once and walk on as someone the story has always contained.
Here is the strange arithmetic of the job: your best night is assembled out of somebody else's worst. You go on because a colleague is hurt, sick, stranded, grieving. The disaster is your cue. There are even universal swings who fly between cities, carrying every version of the same show in their body, arriving wherever tonight went wrong.
I keep deciding it's the opposite of stardom, then deciding it's the truer kind. A star is irreplaceable by design. A swing has spent months making sure that nobody is — that the show can lose any single one of its people and still stand. They rehearse a role they pray never to perform, and when the applause finally comes it's for a seam so clean you'd never find it.