You can learn a lot about Greyscale's new show at the Gate from its subtitle. That's partly because it's extremely long. But it's also because A True Story About the Revolutionary Politics of Telling the Truth About Truth by Someone Who is Not Julian Assange in Any Literal Sense flags up the meta-theatricality and semiotic trickery that are central to the workings of the play. It doesn't tell you everything. It doesn't prepare you for the fact that you'll be given a cup of tea and a biscuit as you enter the theatre for instance – that's crucial too.

The true story in question is that of Evariste Galois, a French mathematician born at the start of the 19th century whose work was important in the development of various branches of abstract algebra. A troubled young man, Galois was killed in a duel at the age of 20, his contribution to mathematics remaining unrecognised until over a decade after his death.

The show's initial set up, in which actors Jon Foster and Lucy Ellinson step into character as Galois and Wikileaks founder Julian Assange, is full of promise. Writers Lorne Campbell and Sandy Grierson (Campbell also directed the show) throw out idea after idea – questions of political philosophy, maths and theatrical convention are all chucked up in the air with apparently little concern for where they will fall. It is ramshackle and funny and the audience interaction is successful in drawing us into this strange piece. Garance Marneur's set within a set within a set is a brilliant physicalisation of the central mathematical concept of the play.

At the point at which Campbell and Grierson begin to try to pull the different strings of the show together, however, Tenet fails to convince. The connections between Galois' story and Assange's are flagged up but not fully enough explored to justify the activist's presence. The reenactment of his extradiction hearing is one of the more powerfully theatrical moments in the piece, and Ellinson gives a nuanced performance, but aside from this scene, Assange is essentially just a narrator.

The maths in the piece is also problematic. While a play like A Disappearing Number befuddles your brain but while doing so fills you with wonder about the incredible complexity of the universe, Tenet merely befuddles. This is partly deliberate, one suspects: knowledge is power and the fact that we do not understand these complex concepts underlines the way in which a figure like Assange has been able to use his extraordinary intelligence to his advantage. But befuddlement can be taken too far, as it is here, making the play so hard to follow that at points dramatic tension is lost altogether.

There's plenty to like about this playful riff on the troubled relationship between truth and meaning, but ultimately there's something about Tenet that just doesn't add up.