It's cheery-making to see how this annual summer season of free theatre, now in its fifth year, continues to develop. Yet for an enterprise keen on all-round accessibility, Helen of Troy is an odd choice.

Without considerable background knowledge about the beautiful Spartan woman who provoked the 10-year siege of Troy, it would be hard to comprehend quite why everyone in this piece is getting so worked up.

The thrust of Euripides's trippy, tragicomic script is that it was all a sick joke on the Gods' part: Helen never really left her husband Menelaus for Paris, but was instead spirited away to a deserted isle. The Helen in Troy was thus a phantom; the war needless carnage.

When Menelaus (Stewart Alexander) arrives, with combat gear and an American accent, it belatedly becomes clear where adaptor/director Phil Willmott is heading: a conflict in the Middle East about something that wasn't there.

The driving home of this message isn't over-subtle, and a couple of the supporting turns are tiresomely broad, but Willmott and his team largely give a good account of both themselves and the tricky text.

Kerry Skinner makes Helen the exact opposite of the "war whore/strife wife" of popular legend and she is ably supported by National Youth Theatre members as a chorus of plaintive priestesses. Challenging entertainment for a dry night.

• In rep until 9 September (morelondon.co.uk).