I wrote it as a mystery as most of my scripts. But then I rewrote it to be more focused on the tension and thriller aspect of it so I just revealed most clues very early instead. Readers seem to miss most mystery elements when they are in the script and not visual. It's hard to really know what a reader can remember from scene to scene in a script that doesn't show you things very clearly on screen.
Locations: Elevator. But also a few exposition scenes outside the elevator that can be moved.
Actors: 1 woman, 1 fit man. And a single small side character.