A lot of productions claim to be immersive theatre and maybe they involve a bit of walking about in the venue to follow the story. Or they boast a nicely dressed set and a surround sound soundscape. Very few pieces of immersive theatre are genuinely that – and leave each audience member with their own unique version of events. But Flabbergast Theatre, with The Swell Mob, have done that with enough bells and whistles to content many a cynical heart.

Enter the Underground (fittingly) at Assembly and you’re transported to an 1830’s tap room, complete with working bar, a surly bank teller, an array of tawdry music hall acts, a hallway of rooms to explore, a boxing ring, a very spooky puppet, and a suitably sinister collection of stuffed animals.

The actors embrace their roles with vigour and commitment, lounging, touting, portrait painting, fortune telling, card trick-ing, regaling and wrong-footing. There’s an enormous number of them: the cast list runs to thirty. I couldn’t swear that all thirty were present and correct but there were certainly far more actors in the room than you’ll see in most Fringe shows. Smoke, sweat, more shade than light and a bustling soundscape give the instant impression of a noisy pub on a busy night. The costumes are gorgeously detailed and the steampunk-meets-goth make-up smacks of Helena Bonham Carter in a Tim Burton movie. In the best possible way.

As the evening progresses, the audience is unobtrusively herded to get drinks, tickets for the boxing match and to place their bets on the match outcome. In amongst the wheeler dealing, lies are being spun, secrets shared and it’s tantalisingly difficult to know where to look. Considered direction from Henry Maynard and Jordan Chandler orchestrates the key moments so skillfully that you can’t help but be there to bear witness. The boxing match between Daniel Christostomou and Dale Wylde in particular is a choreographic masterpiece, suggestive but perfectly effective.

For all the characters you try and track, you sense handfuls more just around the corner. Through trial and error, I stumbled to some sort of conclusion of my version of the story; which isn’t to be cryptic – but the figuring out is part of the fun. For those that stumble in knowing nothing, a bit more direction at the outset would be helpful. From stupid stuff like a designated space to leave your coats and bags through to more fundamental things like your role as visitor to this pub. As once you’ve figured it out, you want all of the 75 minutes to help you in your quest for the —- (sorry).

This production is overflowing with energy, attention to detail, back stories and mysterious, possibly malevolent romance. If the idea of losing yourself in times gone by and unravelling a bit of a mystery while you’re at it appeals, go see, guvnor. As you won’t find much else like it.