I logged into Twitter for the first time in ages this week, and among the overwhelming backlog of breathless announcements, I found one intriguing highlight.  Right now at the Southwark Playhouse, you can see the young theatre group which - almost everyone agrees - laid on the most exciting and innovative programme to grace the Edinburgh Fringe for years.  They're the York-based Belt Up (Nothing To See/Hear).

I wasn't the only reviewer to pick out Belt Up at last year's debut Fringe, though I flatter myself to think I was one of the first.  To be honest, though, it wasn't hard to notice 2008's preposterously ambitious programme; camped out in their very own offshoot of the sprawling C Venues chain, the visiting student troupe delivered a riotously energetic, dawn-to-dusk feast of site-specific, rule-bending theatre.

It was a hard act to follow - but if anything, their 2009 Edinburgh season was met with more enthusiasm still.  Even Lyn Gardner got on board, with the closest thing to a gushing review you're ever likely to find in The Guardian.  And now, it's London's turn to belt up and enjoy the ride, as the still-developing outfit bring their acclaimed productions of Tartuffe and The Trial to Southwark.

I doubt I'll make it down south for the occasion, but I just can't wait to read about how their work's evolved.  And it's prodded me to do something I owe them, and something that's long overdue; to sit down and write a proper retrospective on the three plays they brought to Edinburgh this year.

Fleeting spell

Top of the bill, and earning Belt Up some pretty serious bragging rights, was a cameo appearance at the International Festival.  Yes, that's right - as winners of a newly-minted award in 2008, they joined the likes of Mabou Mines on the pages of Jonathan Mills' invitation-only programme.  We expected something unusual for such a spotlit occasion, and we weren't disappointed.

Performed to an audience standing in blindfolds, Léasspell was a sensory tapestry of sound and touch, where an actor was just as likely to whisper in your ear as to take you into hold and dance.  I recognized it, perhaps, as a "Best of Belt Up" - binding together many of 2008's scintillating ideas into a single package of highlights.  And it was brilliantly matched to its died-in-the-wool official-Festival audience, forsaking the noisier and brasher of last year's stunts for a calm, respectful, slickly-managed atmosphere.

At half an hour, this was always going to be a taster; a tempting morsel to show the International Festival crowd just what they were missing.  But, call me greedy - I'm afraid I wanted a little more.  I loved the experience - craned to hear the whispers, touched the unseen hands, turned my face towards the flashes of half-perceived light.  But the magic faded quickly.  It was an insubstantial sprite of a play, which caressed me and cavorted around me but then, just as suddenly, was gone.

Arresting Trial

In contrast to the exquisite but ephemeral Léasspell, Belt Up's second Edinburgh premiere was rough and robust.  Now playing in Southwark until 28 November, The Trial is a reasonably faithful adaptation of Kafka's last great work; and even months after seeing it, I feel a frisson of excitement at the raw brilliance of this choice.  If anything deserves the disorienting and perplexing treatment meted out by Belt Up, it has to be this parable of justice forever delayed.

Belt Up's big new idea for The Trial was to fill the room with smoke, hiding the walls from view and framing the play in a seemingly infinite space.  It worked to break down barriers between scenes, and heightened the sense of dislocation inherent in Kafka's text; but the downsides of performing in a fog were also pretty obvious, and I'm not convinced that it was truly a good idea.  Still, the cloudy atmosphere enabled some neat tricks of the light, and a few visually arresting images emerged from the murk - as, for example, a group of actors joined forces to play a grotesque but sinisterly human torture machine.

I liked the adaptation, too.  It used the famous passage Before The Law twice: once as an intriguing opening, and then as the jumping-off point for a strikingly re-imagined ending.  But, whisper it quietly... it wasn't really that immersive.  We promenaded around the space, yes, and jostled for position as the actors plunged into our midst.  Yet once the first few minutes were over, I rarely felt more than an interested observer - never truly identifying with Joseph K, nor finding myself complicit with his tormentors.

It would be harsh, far too harsh, to suggest that Belt Up spent more time on the gimmicks than on the theatre.  But it's entirely fair to say that there's a tension here; that the more attention you lavish on the trappings of interactivity, the less room there is for the type of deep engagement which truly draws your audience in.  The perfectly-formed but almost plotless Léasspell was at the extreme end of that scale, yet I've no doubt it achieved what it set out to do.  The Trial, on the other hand, teetered on a tightrope in the perilous middle ground - and to my mind, never quite found its balance.

Missing Molière

I've the same mix of delight and doubts about the last of Belt Up's Edinburgh shows, their riotous parody revival of Moliere's Tartuffe.  Most reviewers deemed their interpretation "meta-theatrical", but I decline to take it quite that seriously; for me, at least, it was thinking man's Carry On, a guilty low-brow pleasure for the dramaturgically informed.

I made it to this one right at the end of the Edinburgh Fringe, and all of us were in an end-of-term mood.  So I giggled with unalloyed good humour as the madcap ensemble bulldozed their way through the wreckage of the plot - hindered at every turn by prima-donna mimes, a living statue with stage fright, an understudy dragged up from the audience and the perpetually drunken Mrs Orgon.

They've taken this one to Southwark too - and, if you can catch it there, you certainly should.  All the same, as Tartuffe implored "Où est le Molière?", a voice inside my brain chimed up: Où indeed?  And if Molière was missing, did I care?  Perhaps I didn't - this time.

Cruel choice

But there's a problem with being an iconoclast: you can only smash each idol once.  I've no doubt that Belt Up's new audience in Southwark will be thrilled by their assault on the fourth wall - just as Lyn Gardner was on her first visit, and I was before her.  But there can't be new audiences forever.  And what brings an audience back isn't the antics; it's the theatre.

So here's the choice confronting Belt Up.  They can sweep the world with the force of a hurricane - but eventually, like any storm, they'll blow themselves out.  Or they can choose to close this chapter and enjoy success in the mainstream; yet the price will be part of their soul.  It's a classic dilemma - and they face it cruelly early in their career.

Or do they?

Let's imagine, for a moment, that they can make the pieces fit.  Imagine - just imagine - the awe-inspiring immersive experience of Léasspell, rebuilt on the solid theatrical foundation of The Trial.  Imagine the breathtaking scale of last year's Macbeth, matched by the restraint and precision they brought to Women of Troy.  Imagine the furnace of innovation quenched by the well of experience... and turning out the finest tempered steel.

I couldn't do it, of course.  I couldn't come close.  But I don't have the talent of these guys.

Maybe, just maybe, they can.