This is devised theatre at a low. Taking stories from the third book of Edmund Spenser's The Faerie Queen, Cligwyn Theatre Company, under director Tom Cornford, has added sound effects, choreography, narrative, music and deep, deep seriousness to create a mess that's far less accessible than the 16th-century original.

It's strange because everything about the piece seems to have been done with clarity in mind. The set is basic - with tables and hat stands serving as doors and surfaces. The six performers can be seen creating accompanying sound effects with the help of microphones. Even a piano has its cover off, revealing the hammers underneath. As with Palladian architecture, you see how everything is done. Unlike Palladian architecture, it's horribly drab.

Plus, knowing how it's done doesn't help us divine what this company think they are doing. Stories start using standard narrative, stories about the female knight Britomart's quest to find her destined lover Artegall, about beautiful Florimell and something: all is lost in the wash of changing techniques.

The dramatic sections rarely convey enough information. The idiomatic, bland improvised dialogue hardly brings you up to speed, and is often mumbled.

Sections of the poem, pre-recorded, are so laden with effects that you can't make out a word of Spenser's already unfamiliar language. But the vague physical theatre is the main culprit. There's loads of it, rarely elegant and never spectacular. When it's done alongside narrative, it hardly adds to the effect. Done on its own, it's baffling.

Then there's the music, by Spesh Maloney. It's good, as it goes - but constant, wrapping everything in a tedious aura of meaningfulness. People gambol around. Sombre music plays. It's as if Stephen Poliakoff directed my little sister's sports day.

• Until 29 December (0844 412 4300) www.sadlerswells.com.