Landscape With Weapon, National Theatre: Cottesloe, London

Joe Penhall was once rightly praised by the director Max Stafford-Clark for possessing the "curiosity about events outside [his] own parish which is essential for a playwright". His last two works, the multi-award-winning Blue/Orange and Dumb Show, created fascinating debates from exploring, respectively, the tricky ethical issues involved in the diagnosis of mental illness and the double standards of tabloid sting journalists.

His gift for entering other worlds and dramatising uncomfortable arguments is again apparent in Landscape with Weapon, his flawed but powerful new play about the arms industry and the moral responsibility of the scientist. The piece is premiered now in the Cottesloe in an immaculately acted, traverse-stage production by Roger Michell that does handsome justice to its lithe intelligence, emotional pain and rueful humour.

Penhall's protagonist, Ned (Tom Hollander), is a brilliant engineering boffin who has dreamt up a super-sophisticated unmanned air vehicle that looks set to revolutionise the nature of warfare. The trouble up to now with flying robots is that they can't be flown inside buildings because they lose contact with satellite navigation. Ned's system enables them, like swarms of birds, to position themselves with total precision by communicating with each other. Henceforth, there will be nothing to stop them from flying, as lethal, uninvited guests, into the cells of rebel militia and the hideouts of enemy leaders.

At the outset, Ned struggles to convince himself that his "paradigm-shifter" invention will be a force for good - whether as a deterrent so psychologically frightening that it won't need to be used or as a method of targeting so exact that it will eliminate collateral damage and civilian deaths. But his considerably less bright, dentist brother, Dan (amusingly played by Julian Rhind-Tutt), sees it instantly for what it is: a weapon of mass destruction. Undermined by his brother's horror and his own misgivings, Ned resists signing the contract when it becomes clear that he will not have full ownership of the intellectual property rights and therefore no means of preventing the United States from re-exporting his brainchild to such allies as Israel. He is then duped into compliance, after which he is betrayed, fired and pursued by the secret service.

You could argue that it's an unfortunate weakness in the piece that Ned seems to start off from a position of extraordinary naivety. "What is wrong with you? Don't you know this stuff? Where did you train - Disneyland?" asks Jason Watkins's incredulous and eerily comic spook. These are questions that will have already occurred to the audience. How could someone so intelligent have put so much faith in Intelligence, or have imagined that it was possible to use American engineers on the project without becoming involved with the American military?

These doubts are to some degree allayed by the remarkable performance of Hollander. A geeky misfit who by the end has become a lonely, haunted and tragic figure, his excellent Ned convinces you that here is a man who has been too wrapped up in Da Vinci-like dreams of discovery. And though sympathies never shift here as unsettlingly as they did in Blue/Orange, the play allows both the spook and the commercial head of the aircraft factory (Pippa Haywood) to pose strong objections to Ned's principles. The former argues that Ned's weapon is a way of hopping over the cowardly civilian shield behind which terrorists barricade themselves. And what is a suicide bomber seeking martyrdom but an unethical "technological solution"?

The ending is bleakly beautiful. Ned had cited the fact that the Koreans have developed a robot sentry guard that blows the head off unidentified visitors. Now, isolated and deeply disturbed, he talks of its virtuous equivalent, Da Vinci's famous toy lion - an automaton whose chest opens and extends the gift of a bouquet of purple lilies. If he were to make one as a peace offering, would anybody accept it from him?

In rep to 7 June (www.nt-online.org; 020-7452 3000)

Interesting? Click here to explore further