Lynne Plowman won a British Composers' award for the children's opera Gwyneth and the Green Knight. In striving to ensure an emphatically adult second piece for Music Theatre Wales, she and librettist Martin Riley have thrown everything into the mix, including sex, murder and the blood and guts of ancient mythology.

Set in 1916, their two-act chamber opera deals with the twilight of the Celtic gods Morrigu and the Dagda - Ma and Da to the lovely Lily and landlords of the seedy Halfway House pub. Condemned for eternity, Ma longs for mortality, wishing to see out her days in, yes, Aberystwyth. Lily's scientific bent risks being warped by the evil Crom, whose cellar experiments with DNA-altering devices and life-essences aim to create ultimate heroes. But Lily's true destiny is tied to Jack, the soldier back from the front, clutching his medal yet damaged by war.

Plowman's eclectic style weaves music hall and patriotic song into darker, more abstracted sounds. It verges on the obvious; nevertheless, there is something beguiling about the fluent writing, equally well-crafted for voices and instruments alike. Plowman is a mistress of theatrical effect, so that the scene where Ma, bidding farewell to her parallel life as a whore, seduces Jack is wittily done, while the moment when Ma and Da admit to Lily that she is not their child has a touching tenderness.

Fiona Kimm's raunchy Ma and Andrew Slater's Da are strongly drawn, with Philip Sheffield making Crom a thoroughly nasty piece of work. Jack is sympathetically sung by Mark Evans. The role of Lily should be key, but, though Louise Cannon is musically assured, too many words are unintelligible. Comedy and gothic horror are sometimes awkwardly balanced, and the libretto tries too self-consciously to be everything to everyone. Overall, though, Music Theatre Wales' usual slickness saves this production from damnation.

· At the Clwyd Theatr Cymru, Mold (01352 755114), on May 31, then touring.