When does political compromise become hypocrisy? How much should moral responsibility impinge on free speech? These are two of the huge questions at the complex heart of the latest work by the sharp-minded and sensitive American writer Christopher Shinn.

Playing out in real time over 80 minutes, Now or Later, in a riveting production by Dominic Cooke, sets up some of the most urgent issues facing Western liberalism and lets them battle it out in the amphitheatre of a US presidential election. With Obama and McCain's real contest for the Oval Office under way, it could not, of course, be more topical. But its brilliance lies in the way in which Shinn marries ideological debate to psychological complexity, shedding light, laser-bright and precise, on the way in which political discourse informs and shapes individual experience.

It is election night, and at Democratic headquarters in a smart hotel there's tentative celebration in the air as reports of victory in state after state flood in on the TV and internet. But, amid the good news, comes word of a breaking scandal: John, the student son of the President-Elect, went to a party dressed up as Muhammad, where he performed a simulated gay sex act on his friend Matt, himself costumed as a prominent Christian evangelist. For John Sr, his wife Jessica and his aides, the solution is simple: his son must issue an apology, and fast. But for John Jr, to do so would represent an unacceptable betrayal of principle.

Motives and morality are fascinatingly impure. Unlike Prince Harry's Nazi armband, John's party garb was intended as a form of political protest - against his fellow students, whom he says are apologists for the most misogynistic, homophobic excesses of extreme Islam yet espouse liberal values. But it emerges, in his conversations with Matt and thorny exchanges with his parents, that his homosexuality and his father's political ambitions have contributed to a painful rift in family relations. Forced from childhood to follow a party line at home, John rebels against toeing it publicly, for reasons that range far beyond the theoretical. His naivety in imagining that his behaviour need not have damaging consequences is tinged with wilfulness. Meanwhile, there's a suspicion that the shift to the right that his father has performed to win conservative votes - euphemistically referred to as “triangulation” - masks some genuine reactionary sentiments.

Cooke's production is thrillingly paced, effervescent with wit and intelligence and superbly acted, in particular by Eddie Redmayne as the unhappily divided John and Matthew Marsh as his father, his every word carefully weighed but concealing an unnerving ruthlessness and volatility. This is highly accomplished work, thrillingly connecting the intellectual with the visceral, the abstract with the human. Urgent and unmissable.

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