Gethsemane, NT Cottesloe, London

David Hare is on strong form with his latest state-of-the-nation play, but the story threads don't all tie up

The Home Secretary is stubbornly refusing to resign. Her husband is facing charges for dodgy business deals abroad and there's been a cover-up regarding their druggy teenage daughter, Suzette, which might soon be exposed by the press.

The plot thickens in Gethsemane, David Hare's latest state-of-the-nation play. Bit by bit, we glean that Otto Fallon (Stanley Townsend) – tycoon, party fundraiser and chum of the PM – has been involved in the cover-up. He was made a governor of Suzette's private school in advance, a fact unknown to the minister herself, Tamsin Greig's tense, steely Meredith, but orchestrated by her aide, Monique. A dangerous journalist, Geoff, is also in Monique's sights because he has rubbed shoulders, and considerably more, with Suzette.

Oh, and did I mention that Otto has suddenly employed an ex-Home Office underling – Daniel Ryan's possibly naive Mike Drysdale? Mike is married to Nicola Walker's Lori – Suzette's ex-teacher and mentor – whom Otto tries to recruit too. The Drysdales are, at heart, old-school socialists with moral consciences, yet they're getting desperately disillusioned and mixed up in this questionable business. The Gethsamane of the title, the dark night of the soul, is theirs.

Hare is on far stronger form here than he has been of late. Directed by Howard Davies, Gethsemane combines menacing dramatic suspense – as well as flashes of sardonic humour – with a bigger ethical worry which touches a nerve: namely, that politicians, corporate magnates and the press are excessively powerful and entwined. You might say Hare is our Harley Granville Barker for the Noughties.

Nonetheless, there's something peculiarly unsatisfactory about this play. Some might complain that it's already out of date with its indirect allusions to Tessa Jowell and Tony Blair. Hare, incidentally, insists this piece is "pure fiction". His made-up PM, Anthony Calf's Alec, is portrayed as a keen squash-player with a drum-kit.

Where I felt cheated was in the supposed machinations of the plot. Much suspicion is brought to hover over Hare's characters, but we never really get to the bottom of anything. Maybe that's his point, but I ended up feeling short-changed. Do all the story threads really make sense or tie up? Odd elisions enhance the sense of mystery yet are a con. Meredith looks beadily at Otto in the final scene, as if she's finally rumbled whatever his game was with Mike and Lori. Whether or not she has, I'm still in the dark. Davies introduces additional hints of past or potential sexual liaisons which lead nowhere either. Still, what you get is an intriguing sense of human complexity and moral ambivalence. The cast are mostly tip-top. Townsend is riveting as Fallon, overbearingly burly with a music-industry pony tail. You're never quite sure if he's affable salt-of-the-earth or a cold sardonic manipulator underneath.

Pip Carter as his spindly, camp major-domo is scintillatingly droll and unnervingly acidic. Jessica Raine has a destructive edge as well as being horribly funny as the stroppy Suzette. Meanwhile Greig – superbly hitting her stride as a serious actress here – quietly reveals the maternal chinks in Meredith's armour.

Runs to 24 February (020-7452 3000).