If you think that Hansel and Gretel is a gentle, happy piece of Christmas cheer, the first act of Lewis Reynolds's pub production for Open Door Opera might give you pause for thought. The children may be naughty, but they're genuinely starving, and the mother may be overbearingly harsh, but she is genuinely at her wits' end. Trimmed of its orchestral lushness to the sound of a single piano, Humperdinck's score acquires a biting edge and focuses you on the subtleties of its harmonic shifts and the joys of its constantly changing rhythms: in spite of its heavy folk music underpinning, it sounds rather more modern to my ears than its 1890s date might suggest.

Reynolds's new translation works well, his direction is constantly inventive and he brings out some splendid acting performances from his young cast. Especially notable were Katie Slater and Rebecca Dale as the children, bringing out a wide range of naughtiness alternating with trying to be good, sibling rivalry alternating with love, and just plain hunger. Dale plays Gretel's dream in Act II in slow motion dumb show as she turns the milk from the restored jug into angels' wings for her mother and father: it was a remarkable piece of theatre which bowled me over.

The King's Head Theatre isn't the easiest venue: the sound isolation isn't perfect, a tiny stage and shallow seating rake can result in it being difficult to see the action (depending on where you're sitting), and watching the house manager cram everyone into their seats was a floor show in itself. But it did have the advantage of a good Yamaha baby grand, which was played with real feel by Open Door's music director Kelvin Lim. It's a challenge to maintain interest in an opera piano score for a solid hour and a half of music, and Lim managed this with excellence.

Having said this, I was less than perfectly convinced by the first act. Lim took it largely at one pace (fast) and one level (loud), and all the singers found it a little hard to compete. The exception was Oliver Gibbs as the Father, who has a huge voice which will undoubtedly be filling much larger spaces at some point. But Lim brought the level and tempo right down for the Sandman's lullaby in Act II, which Rosalind Coad sang beautifully. After that, he never quite returned to the initial manic speed, and the music was much the better for it. As the story lightens up from the horridness of the first act to the pantomime of the second and the joyous ending of "The witch is dead", the balance between singing, acting and piano became just about perfect and I was thoroughly won over.

This production reinforced for me (if reinforcement were needed) how much I enjoy listening to opera in very small spaces. In spite of the lack of orchestra and the inevitable imperfections, the immediacy and reduced vocal strain give this production a big lift, vocal quality was broadly good and the acting top notch. There weren't many children in last night's audience, but I saw one little boy who can't have been more than five, totally entranced. I wish him many happy years of opera going.