Nell Leyshon's Glass Eels, a mildly preposterous drama of unhappy family relations in rural Somerset, comes dressed up in lashings of flamboyant symbolism. Artificial streaks of lyric poeticism confound the otherwise stolid bleakness of people's conversations.

Miss Leyshon won an Evening Standard Most Promising Playwright award for Comfort me with Apples, a remarkable, expressionistic vision of rural life, in which psychological and economic pressures tragically converged in the life of a bereft farming family.

Glass Eels, though, bothers itself little with conflict, development and change. Miss Leyshon vainly attempts to imitate the form and poetic diction of one of Lorca's rural tragedies, while borrowing inspiration from Tennessee Williams's heroines, who try to ease pangs of sexual hunger with the wrong men.

The action takes place by a river, in a home so run-down that symbolic water flows through the house. In a miniature pool, Laura Elphinstone's tense, mother-lorn teenage heroine, Lily, who has the hots for Tom Burke's gloomy, thirtysomething Kenneth, cools her fuming libido, escapes her retired undertaker, grandpa, ever-hungry Harold, and her widowed father, Mervyn, who almost imprisons his daughter in the house.

Although both Lily and Kenneth serve as quasi-partners to widowed parents ,nothing is made of their shared, precarious status.

Mike Britton's expressionistic set, with a vast, shattered mirror that variously reflects characters on stage and sombre views of the countryside beyond, is bathed in emphatic murkiness. The symbolic eels of the title, representing sexual energy and things repressed, are poised to stir from the silt and return to the sea. It is very hot, and people, true to Leyshon's repetitive-strain dialogue, keep issuing irritating weather commentaries.

"Hottest I known it here. Yeah, hottest I known it. Mind, least the water'll be cool," says Tom Georgeson's obstinately unamusing Harold.

Possible challenges to family stasis come far too late when Lily expresses jealous hostility to her father's girlfriend Julie (Diane Beck) and attempts Kenneth's aquatic seduction.

An inappropriately subdued encounter between Phillip Joseph's Mervyn, guilt-struck over his wife's death but now accepting he must let his daughter go, imposes rather than struggles towards a solution of family problems.

Lucy Bailey, always such an exciting and inciting director, here condones acting of languid glumness. Even when the river floods and a window is smashed in a final symbolic outburst the effect is oddly bloodless.

• Until 26 July (020 7722 9301).