13, National Theatre: Olivier, London

(MARC BRENNER)

Mike Bartlett's ambitious new epic, 13, is set in a not-so-alternative present-day world of street protests and economic misery where Londoners repeatedly awaken from identical nightmares of disaster and a female Tory Prime Minister (Geraldine James) ponders supporting a US-led invasion of Iran.

A charismatic young man, John (Trystan Gravelle), returns home after several years' absence and starts to preach an anti-materialist gospel of belief – not in any God but in the transformative power of belief itself. Gradually, a peace movement gathers round him.

The first half introduces us to a host of characters (boorish, renegade solicitor; star atheist don; academic protesters against student fees et al) and Thea Sharrock's vividly acted production keeps impressive control of the overlapping Altman-esque strands, generating an ominous sense of interconnectedness. One of these figures is a precocious, 11-year-old bookworm who recoils from the idea of reading Harry Potter and reminds her diplomat father of the hundreds of protesters slain by the Syrian government and the thousands of children starving in the Horn of Africa. "There's so much evil in the world. I don't have time for fun."

There are moments when it is tempting to equate this child with 13 itself. Occasionally, you feel that the play is so busy taking on the big issues that it has no time for such lesser tasks as arousing genuine emotional involvement or establishing political plausibility. Bartlett wants us to see the attractions and the dangers of politics driven by religious faith and of the agitation for change that is mobilised via Facebook and Twitter rather than the ballot box. But it strains credulity to accept that a mild idealist with a programme as vague as John's would be able to rally such a powerful campaign for peace. Of an elected opposition, there is no mention, while, bafflingly, the PM herself appears to bypass Parliament in a solo decision to go to war.

In the three-cornered set-piece debate in the second half, her atheist academic friend (Danny Webb) has some lively, politically incorrect thrusts against John's idealism: "We cannot allow men we wouldn't trust with our sister to have access to nuclear weapons." But all these people are essentially mouthpieces. The awkward attempts to marry the personal and the political – as when John's shadowy role in the accidental death of the PM's student son is raised to cast doubt on his messianic tendencies – merely emphasise how hard it is to care about any of 13's multiplicity of characters.

In rep to 8 January (020 77452 3000)