“Next to Normal” is a no-nonsense story of how the mental illness of just one person can derail an entire family. Bipolar disorder isn’t usually something to sing about. But here’s the thing: “Next to Normal” is a musical. A rock musical. And it works beautifully.

You can see for yourself at Mill Mountain Theatre’s intimate Waldron Stage, where the show is a very good fit. But hurry: It closes Saturday.

Credit is due a fine cast and especially the rousing multi-style music of Tom Kitt and Brian Yorkey’s lyrics. The latter are touching, funny, a little dirty and always informative about the show’s vexing subject. “Next to Normal” won a Pulitzer Prize in 2010.

The directly afflicted, in this case, is a housewife and mother named Diana Goodman (played by Amy Baldwin). She lost an infant son 16 years earlier but has never shaken the depression and erratic behavior that followed. Her doctors mention bipolar disorder, but, as Diana puts it in one of the show’s many affecting tunes, that doesn’t begin to cover it.

Long-suffering husband Dan (Chris Gleim) and daughter Natalie (Mikayla Cohen) beg Diana to put the death behind her and return to a life that is at least “next to” normal. “He’s Not Here,” Dan sings. But Diana won’t or can’t do it.

Baldwin and Gleim, the show’s professionals, are polished singers and actors. Baldwin’s resonant voice is especially striking on slower solo passages.

Gianni Palmarini, a member of MMT’s Apprentice Company, plays Natalie’s weed-loving romantic interest, and Briar Boggs plays both of Diana’s doctors. Along with Cohen and Jake Ellsworth (who plays Gabe), Palmarini and Boggs are college theater majors. Travis Kendrick directs “Next to Normal,” and Seth Davis leads the show’s tight six-piece combo. The Actors Equity production stage manager is Jessica Taylor Edwards. Matt Shields designed the attractive and efficient set.

The music is more or less nonstop in the two-act show, even during the rare pauses for spoken lines. But the more than 30 songs (including reprises) move briskly toward an ending that, if not exactly upbeat, offers at least a hint of hope for Diana, her family and real-life fellow sufferers.

Showtimers mounted a praiseworthy version of the same show just a couple of months ago.

Though you would hardly know it from some of their better efforts, Showtimers is quintessential community theater. The actors and crews are theater-loving amateurs.

Mill Mountain shows generally are the work of professionals or aspiring professionals — and, of course, it shows.

’Nuff said. The two productions don’t bear further comparison. Just think of the current show as a second chance for valley playgoers to enjoy an exceptional musical.

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