I say drama because the presentation goes beyond a mere comedy routine in its fluid arrangement on a bare stage with six red chairs, its mood changes, light and darkness, and the complementary physical suppleness of Marlowe and Young, identically clad in plain black trousers and zipped up hoodies.
They create a world of danger and sadness in their cast of chatterboxes, foul-mouthed teenagers, pregnant women fighting for the last seat, mother and daughter making it up, career girls on a night out, even an office worker coming alive as an after-hours drag queen in high heels.
This is the opposite of Cliff Richard - who's innocently referenced in the show - going on a summer holiday on that cheery double-decker. It's a similar process of escape, but into darker, more private areas where the night bus becomes a place of refuge, a point of contact, a sanctuary as well as a hell-hole.
Marlowe skims across her familiar expressive range, always so vivid and arresting, while Young - perhaps best known in Edinburgh for Julie Madly Deeply and Cabaret Whore - proves herself an actor of genuine versatility and skill.
Night Bus runs at the Pleasance Courtyard until 25 August