Gilbert and Sullivan operettas occupy a space betwixt and between, a genre unto themselves.

They are not, as the name implies, little operas. They are of comparable length and their leads require fully operatic voices, but they are not operas.

They are farcical and fluff, with spoken dialogue, light-hearted tunes and parts for semi-trained voices. And yet, neither are they musicals.

Performers must be able to inhabit both worlds, equally strong in singing, when characterization relies on their voice, as in acting, when there is no music to help carry the scene.

In many ways, G&S operetta is one of the most demanding of genres and, consequently, one of the most entertaining.

Continuing the summer operetta "tradition" begun last year, Hawaii Opera Theatre has opened Gilbert and Sullivan's immortal "The Pirates of Penzance," directed by Henry G. Akina, designed by Peter Dean Beck and conducted by Michael Ching — HOT's A-B-C team.

The plot revolves around Frederic, who as a boy was apprenticed by accident to pirates and who has remained loyal to them, bound by his unfaltering sense of duty. On his 21st birthday, his apprenticeship over, he severs ties with his unsavory past and sallies forth to return to respectability, armed chiefly with innocence.

But alas! His sense of duty makes a mess of the matter, binding him betwixt and between, as well. He is bound both to the love of his life, Mabel, and her extensive family, and to the pirates, orphans all and hopelessly tender-hearted, who turn out to be ... ah, but the end is best a surprise.

Akina bypassed the contemporizing and political updating G&S productions often receive, adding only touches of local color and taking a few discrete nips and tucks in the score. Only the famous patter trio, "It Doesn't Really Matter," was sorely missed.

Akina also recapped several of his directorial trademarks, including a sumo wrestler (Onipa'a Pa'a'aina) lifting the curtain and a recurring sight gag, this time a mermaid (Stephanie Sanchez) who has to be carried around the stage.

The most memorable aspect of the production, however, was Akina's cast.

Curt Olds was back, this time as the Pirate King, and just as entrancing as last summer in both singing and acting. Although his first solo lay too low for his voice, the rest seemed written for him, his light, firm baritone creating a most civilized rogue, handsome and uniformly charming.

Tenor George Dyer (Frederic, a Pirate Apprentice) and mezzo Jean Stilwell (Ruth, a Piratical Maid-of-all-Work) rounded out the central trio with excellent voices and strong acting, creating one of the evening's high points, the "Paradox" scene.

Each contributed individual high points as well: Stilwell's opening solo, and Dyer's comic wooing of the maidens.

Korliss Uecker (Mabel) had a large, operatic soprano that set her apart from the rest of the cast, a fact that Akina could have exploited for greater comic effect. Her "Roundelay" and her "Poor Wand'ring One" vocalizing sparkled with touching delicacy.

Michael Gallup made a bumbling and lovable old fool of a Major-General, with good timing in comic exchanges (as in the "orphan/often" mix-up), and a lovely lyric bass (as in his "Sighing softly" song). Unfortunately, his voice lacked the agility to maneuver the character's trademark "Modern Major-General" patter song, and his weak enunciation obscured Gilbert's brilliant verses.

Among the supporting characters, Mary Chesnut Hicks (Edith) stood out, not only for her large, increasingly polished soprano, but also for her exceptional acting — exceptional even when she is not singing, a rare quality in musical theater.

The one casting misstep was Frank De Lima (Sergeant of Police), whose more intimate comedic style was lost in the large hall, and whose pleasant singing voice was out of place and overwhelmed by all the operatically trained voices.

Throughout, and not surprisingly, the production excelled with lyric numbers and faltered with patter songs, whose very rapid delivery of notes/text is far beyond merely "difficult."

Akina's staging proved especially delightful in Act 1, abounding with witty touches and vividly realized scenes. In Act 2, however, that momentum seemed to wane as missed opportunities accrued.

Act 2's structure is a dramatic crescendo, slowly adding characters, choruses, and complications. At its peak, when it becomes apparent to all that there is no way out of the mess, the Sergeant of Police "solves" it with politically correct but completely illogical nonsense.

That moment is the work's grand joke, poking fun at society's (lack of) reasoning. It was a moment that could have been more clear. Fortunately, waning momentum is one of the things that can change as a performance settles into its run.

Anne Namba's costumes proved a hit, flooding the stage with color, enhancing characters, and creating a very dashing Pirate King.

HOT's chorus, a few insecure passages aside, provided a solid musical foundation, and their paean to poetry was beautifully resonant. Their lively enthusiasm contributed much of the show's energy.

Conductor Michael Ching navigated with a firm hand through occasional tugs of war, missed cues, and rough waters to deliver an overall delightful performance.

Ching's overture was particularly lovely — light and airy, with a gorgeous transition solo by oboist Scott Janusch.