David Hare’s new play is one of his very best and easily the best play of the year. It draws on aspects of contemporary public life – and characters – to weave a beautifully plotted drama of lost idealism, hypocrisy in journalism (“mockery oils the wheels of democracy”), political party fund-raising and, especially, the scandal of the systematic demoralisation of teachers.

The play’s title refers to Christ’s night of doubt in the Garden of Gethsemane. Only Lori Drysdale (Nicola Walker), a former teacher who is now busking at Baron’s Court, has seriously questioned her own mission statement. Others are holding this process at bay: Tamsin Greig’s business-like Home Secretary, Meredith Guest; Stanley Townsend’s pony-tailed, squash-playing Labour Party fundraiser, Otto Fallon; Adam James’ muck-raking journalist Geoff Benzine, an academic medievalist who slipped into Fleet Street after writing a couple of book reviews.

At the centre of the play is Jessica Raine’s scowling Suzette, Meredith’s daughter, who was unhappily moved from her comprehensive (where Lori taught and befriended her) to a “good” fee-paying school where she’s been caught out in an escalating drugs and sex scandal. Unknown to her mother, the Labour Party has installed Otto as an unseen fixer to try and divert press attention. Meanwhile, Suzette's unseen father is embroiled in financial misconduct charges abroad.

You can reference in all this real-life parallels with Tessa Jowell and her husband David Mills, with the smooth operations of tennis-playing Lord Levy, with a Home Secretary’s (Jack Straw’s) son landing in trouble and – when Anthony Calf’s drum kit-bashing, money-loving PM pops up to try and persuade Meredith to call off, or at least cool off, her marriage – you can note allusions not only to Tony Blair but also the late Robin Cook fracas when he was issued with central office directives on his private life.

But this is not a play like Alistair Beaton’s satirical, Blair-bashing Feelgood. It is stamped with moral seriousness, freighted with complex argument, yet gleaming with absolute theatrical clarity. Gethsemane is also far superior to Christopher Shinn’s recent Royal Court premiere of Now or Later (in which an American president’s son causes difficulties on election night) because Hare’s canvas is larger, his ambition greater, and he takes the pulse of a nation seemingly inured against the vulgarity which engulfs it. Otto, smarmy and ignorant, once a hairdresser in Hendon, becomes chairman of Covent Garden; says it all, really.

Crucially, both Meredith and Lori find goodness and strength in their lives. And Lori’s husband (Daniel Ryan), a former Home Office civil servant, makes a crucial journey from Otto’s employ to bitter critical analyst of the whole tawdry system. There are lovely cameos from Pip Carter as Otto’s camp, canapé-wielding gofer and Gugu Mbatha-Raw as Meredith’s wise and gorgeous PA.

Bob Crowley’s design is a brilliantly adaptable grey squash court on which Howard Davies’ probing, icily authoritative production is immensely enhanced by the flashing cityscape projections of Jon Driscoll and Gemma Carrington, the witty musical melange of Dominic Muldowney and sound designer Christopher Shutt, and the truly outstanding costumes (not for the first time this year) of Fotini Dimou. An exhilarating, triumphant evening.

- Michael Coveney