Laureen E. Smith in The Piano Teacher at Rep Stage. (Britt Olsen-Ecker)

Don’t be fooled by the sweet little old lady nattering innocently as she offers cookies to audience members in the front row at Columbia’s Rep Stage. Mrs. K, as the retired piano teacher was called by her students, may seem harmless, but the 2007 drama in which she’s the central figure — Julia Cho’s “The Piano Teacher” — is driven by a heart of darkness.

Not that dear Mrs. K. has adolescent bodies buried in the basement of her quiet, old-fashioned home. But something happened years ago as she taught Beethoven and Chopin to kids whose feet didn’t reach the floor as they sat on her piano bench. And what happened was, as Mrs. Lovett delicately says to Sweeney Todd, not very nice.

Cho’s script has been described as a chiller, and it certainly has the throwback style of a vintage mystery. As Mrs. K, Laureen E. Smith — dressed in a dull floral dress and a drab cardigan — simply sits in her chair and talks to us for the longest time. Smith and director Kasi Campbell play it cool, allowing Cho’s script to lull us into a comfortable sense of security.

Eventually, Cho starts turning the screw, for better but also for worse. The intrigue ratchets up when Mrs. K, bored now that she’s retired and her husband is dead, starts phoning former students. Where can this lead? The awkwardness sets up clever comedy when she rings up an ex-student named Mary (played with an amusing blend of politeness and confusion by Kashi-Tara), now grown and with two kids.

By that point, though, you’re not thinking about Mrs. K anymore, but about the unseen Mr. K, who once upon a time escaped the kind of wartime horrors that scar a mind for life. Mention of Mr. K seems to make Mary feel oddly creepy. And in the unremarkable, everyday world Cho establishes — we never leave Mrs. K’s humble living room, furnished by set designer Daniel Ettinger with little more than a stuffed chair and an old piano — the slightest rough-edged detail stands out like a drop of blood on a white doily.

Naturally, you start guessing at the big dark secret that will inevitably be revealed when the play’s third performer finally arrives. As Cho’s theme tiptoes into territory more vigorously explored by Martin McDonagh’s “The Pillowman,” you won’t be far wrong.

It’s not as suspenseful as you would hope, and Cho’s conclusions don’t have the air of inevitability. But “The Piano Teacher” is impressively patient and still fairly crafty, and there’s no faulting Campbell’s calm production or the cast’s very clean, unhurried acting. Mrs. K probably does two-thirds of the play’s talking, yet Smith resists any temptation to turn it into a showy part. Smith’s patter isn’t flighty or fussy; her approach is low-key and persuasively normal, as non-threatening as that ever-present plate of cookies.

Control is the watchword for Kashi-Tara, too, and for Joshua Morgan, who makes a late appearance as one of Mrs. K’s most promising students. The show’s 90 minutes unfold in tight harmony, even if its big rumbling minor chord finish is not completely convincing.

The Piano Teacher

By Julia Cho. Directed by Kasi Campbell. Lights, Marianne Meadows; costumes, Jennifer Tardiff; sound design, Chas Marsh. About 90 minutes. Tickets $33-$40. Through Feb. 23 at Rep Stage, 10901 Little Patuxent Parkway, Columbia. Call 443-518-1500 or visit