If the minimalist trend in stage sets continues this season, soon they're going to disappear entirely. Latest case in point: Tajemství (The Secret), in which a tilted platform and a handful of projections fill in for a village, castle and alderman's home. Great leaps of imagination are required to fill in the details, and the same might be said for the opera itself.

Tajemství is Bedřich Smetana's seventh opera, composed in 1877, when he was in failing health and had been deaf for nearly three years. Smetana left the choice of subject matter entirely up to his librettist Eliška Krásnohorská, with whom he had collaborated on a successful previous opera, Hubička (The Kiss). She chose a romantic comedy set near the famed Bezděz Castle in northern Bohemia, where Smetana had a summer home.

The story is a parallel tale of two sets of lovers. Kalina and Rosa missed their chance for happiness 20 years earlier, when Kalina was rejected by Rosa's parents for being too poor. Now Kalina's son Vít faces similar obstacles courting the lovely Blaženka. Kalina gets a chance to set everything right, if he's willing to venture underground in search of a secret treasure promised by a dead monk.

Photographs of previous National Theater productions of Tajemství show a full-blown village with the castle hovering in the background. Budgets being what they are these days, not every show can get that kind of treatment — but, in this case, it certainly would have helped. There's no context on the spare stage, no sense of the historic setting and village lore and threads of Catholicism and superstition that form the underpinnings of the story. Cast adrift, it relies entirely on the music and singing.

Which are good. The seven main singing roles are well-balanced, so there was no clear standout on opening weekend. But the singers, mostly house regulars, were uniformly strong, with some particularly bright moments from Vratislav Kříž (Kalina), Jana Sýkorová (Rosa) and Jiří Sulženko (Boniface). The orchestra, under the baton of Zbyněk Müller, sounded crisp and lively, lending some fine shadings to the shifting emotional nuances of the music.

If the singing and music are strong in an opera, that's usually enough to overcome weaknesses in the sets. So why this production never develops any legs is puzzling. Whether because of the staging or the direction or the story line — or a combination of the three — Tajemství just never jells. It's more like a rehearsal with many of the right elements in place, awaiting the final spark that will pull it all together.

The length hurts as well. There are two intermissions that stretch the running time to two hours and 45 minutes, too long for such a light piece. The addition of a couple props necessitates the second intermission, but it makes the final act, at only 20 minutes, seem anticlimactic.

Perhaps the most telling reaction to Tajemství came during one of the intermissions, when the regular coterie of elderly Czech women who sit in the balcony like Madame LeFarge could be heard dismissing the production as sekaná, the chopped-up leavings of meat.