One thing that playwright David Greig cannot be accused of is a lack of ambition. His new play Dunsinane not only chooses to start at the point where Shakespeare’s Macbeth ends, but switches the mood to offer us a vibrant and witty comedy, albeit one with a dark heart. Added to all of this, Grieg brings Lady Macbeth back from the dead, gives Macbeth a new heir and offers an inflexibly principled Englishman to negotiate the resulting chaos created by the pretenders to the throne.

The comedy created by the clash of nationalities is beautifully observed. Siward, the English commander, becomes ever more frustrated by the mutable Scots aristocrats around him who work by an entirely different moral code, as lax as he is rigid. Performances by a largely new RSC cast are very good. In particular, Siobhan Redmond as Gruach is fantastically mystical, but all the actors make the most of some beautifully turned one-liners and wry observation.

There is also a tragic strand to the play that examines the nature of war. Scenes of boys far from home, surrounded by mystifying tribal politics, ambushes, hostile mountains and confusion over their mission, seem to recall Iraq and Afghanistan. In one archly paradoxical scene Siward is forced to reveal that he is escalating the fighting in “pursuit of peace”.

What is most impressive, though, is that this parallel to the modern world is delivered with the lightest of touches, by small tragedies and a gentle but incisive humour – the audience aren’t being told what to believe, but are being challenged to think.

To take on so much in a single play is a large gamble. The shifts of tone, the deviation from the mood of the Shakespearean source, the nod to Britain’s current conflicts could all have fallen short. Instead, the play is an impressive achievement, simultaneously showing us two time frames, two genres, two nations.

Until March 6. Box office: 0207 722 9301 (www.hampsteadtheatre.com).