Immersive theatre is useful for two things: its way of messing with theatrical norms is what we think of first, yet it is equally valuable when you turn its power on the audience. What, for instance, does a suited businessman look like at 6.30 in the evening, below Waterloo station, at the beginning of a play that sees his lower half accosted by the performers he thought he’d come to see on stage?

Those that call themselves Gruff Theatre, here at Vault Festival for Instructionally Invited, answer my prayers during this production by telling me exactly what this man would look like. Though, mostly I couldn’t look for fear of screaming in aghast awkwardness myself. It’s this kind of frivolity: the leg-grabby, people hidden in corners – SURPRISE! – kind that Gruff build their play upon, splitting us poor things into groups of girls and boys, sweeping us off into courting rooms and holding rooms in a manner house from no particular time period and with little to offer guests – just a satirical poke at party throwing in the upper classes.

Photo credit: Richard Davenport

The acting is ballsy, the characters gawdy , their interactions classically timed with pomp and intelligent satire that pins these lonely hosts as mad eccentrics. The mood is upbeat and the irony precision-timed to get real laughs out of this – a play that passes the Vaults as an upper class living space. How hideous this pompous lot are, and in this, caricatured brilliance forms.

The only semblance of plot politely ties the latter ends of the play together by reuniting the audience’s men with the women over card games and dinner. Then we’re all thrown out the door we came in from. Though one piece of immersion that saw a male actor thrust his head into a ladies’ lap took the stunt uncomfortably far, the rest is built of well measured creative drive: our headless tour around this grotesque mansion doesn’t reveal much about its subjects, but it is a hilariously put, straight forward and rollicking skit.