I.D., Almeida, London<br></br>Democracy, NT Cottesloe, London

The best - and worst - way to tackle history

At first glance, the new plays I.D. and Democracy are almost twins. Both have at their core a political prophet who realised a basic moral truth long before the society he lived in. Demetrios Tsafendas, a displaced nomad who ambled from country to country seeking an identity, saw that South African apartheid was a preposterous monstrosity and assassinated its architect, Prime Minister Hendrick Verwoerd, in 1966. I.D. is his story. Chancellor Willy Brandt saw that a divided Germany and a divided Europe were a disaster. He returned from safety in Norway, where he lived out the Nazi years, to fight for a reconciliation that only came long after he left power, in 1989. Democracy is his story.

Only one of the plays is a success. In the wildly overpraised failure at the Almeida, I.D., the story of Tsafendas is a genuinely interesting one: he had a mixed racemother but was classified as white by the apartheid system. In South Africa, after a life of aimlessly wandering the globe, he met Helen, a black South African woman with whom he had been corresponding for years. He wanted to marry her, but when she discovered his background she panicked. For a moment the play (direced by Nancy Meckler) flickers into life as it shows, through the character of Helen, how tyranny works: by forcing people to internalise its absurdities.

Helen begins to call him "Master", as she was legally obliged to address all white men. She finds Tsafendas's attempts to show that racial categories mean nothing incomprehensible: "The Church says it too, it's even in the Bible," she cries, "in the Tower of Babel story. God himself is warning us, so pardon me but, I know, who are you to come here and say anything different?" This moment works theatrically because it shows us something new, something we didn't expect.

Otherwise, the themes explored by Antony Sher - who wrote the play and takes the leading role - are beating-you-about-the-head obvious, and have been investigated far better elsewhere. You only need to list them to realise how familiar these ideas are: Hannah Arendt's notion of the banality of evil (the white south Africans are really, really stupid. And boring); that sociologist's favourite, the fragile and arbitrary nature of "racial" and national identities (yes, Tsafendas doesn't really know where he's from!); Michel Foucault's old obsession, the lunatic as sage. Ho hum.

This last theme has at least a nice theatrical touch to illustrate it. Tsafendas was convinced that a tapeworm he picked up as a teenager never left his body and was always talking to him, so Sher has the tapeworm appear in the form of an excellent Alex Ferns as a crazy, fascistic bad conscience, dressed in slimy suits and swimming goggles. It is fair to say that he is the best tape-worm I have ever seen on stage.

But even this device is milked so hard that the udder bleeds. When the new post-assassination Prime Minister is told about this delusion, he says, "Either he's mad, or we are." We get the point! There's even a joke about a man called Pratt. And it goes on for about a minute. That's how low the script sinks and how badly it stinks.

Yet there is a deeper failing in the play, and it is one that stalks most plays that tell "real life" stories. They tend to derive their narrative force, not as all good plays do, through the internal dynamics between and within their characters, but through the force of external events. It is blindingly obvious that the play is building up to the assassination, yet the characters are constrained from their first second on stage to follow that course, to be "real" according to historical record rather than dramatically real.

Also, politically, the play suffers from a painful lack of ambiguity. I wager that not a single audience member trekking out to Islington will be pro-apartheid. The moral limits of the play are, then, so obvious from the beginning that it can only ever be an act of political self-congratulation. Of course there is a place for that, but there has been in London theatre a surfeit of this lately: a distasteful nostalgia for the battle against apartheid, which was black-and-white in every sense.

Nobody could accuse Democracy of being unchallenging. Michael Frayn's new play is so unashamedly highbrow (like his previous play, the masterpiece Copenhagen) that at times he almost seems to be defying his audience to lose concentration with long, dense descriptions of the exact make-up of Willy Brandt's coalition. Amazingly, the writing is so vivid that this never happens.

Wisely, Frayn has picked one aspect of Brandt's life through which to refract his story; a blessed relief from Sher's unfocussed attempt. And what a story it is. It turns out that at the very heart of the Chancellor's office for four crucial years, his right-hand man, Günter Guillaume, was a spy planted by the East Germans to report back every detail of Brandt's life.

Like Copenhagen, the play opens with a character, this time Günter, trying to retell his story as it happened. The relationship between the two men - who were both womanisers who grew up without a father, both eternal strangers in West Germany - develops gradually into one of mutual dependence. Günter wiped Willy's jacket free of dust, fluffed his ego before a big speech, kept his women in line - and in return, Willy gave Günter not just information but friendship too. Their families even holidayed together.

Frayn uses democracy as a dazzling extended metaphor that rages around the play like a lion - it's amazing to watch and you never know where it will leap. Democracy is, throughout the play, pulling itself apart (Brandt's coalition is unstable), just as each individual is always pulling him or herself into contradictory pieces. Frayn seems to see this as problematic but unavoidable. We all - all his characters, all people and all countries - break down into contradictory fragments; democracy is the only way to manage this endless fragmentation.

This is how he chooses to depict the bizarre betrayal by Günter (slightly over-played by Conweth Hill in director Michael Blakemore's otherwise perfect cast). He was a divided man, one half loyal to Brandt (Roger Allam), the other a traitor, and his two sides simply can't be reconciled. To look for meaning and coherence in Günter is to miss the point: he could, like us all, hold two perfectly contradictory views at the same time. "I am great, I contain multitudes," says Brandt, quoting Mark Twain's explanation for his own incoherences. Brandt and Günter do not quite make sense, and that is partly the point.

When finally Germany is reunited in a stunning theatrical sequence, Brandt's claim that "our divided self has become one self" doesn't quite ring true. Division is the natural state of humanity (if not Germany), Frayn seems to say; the question of Democracy is how we manage the fracture lines that run through our country and ourselves.

'I.D.': Almeida, London N1 (020 7359 4404), to 18 October; 'Democracy': NT Cottesloe, London SE1 (020 7452 3000), to 30 December