At once, mesmerizing and spare

Singer-songwriter Beth Orton performs in the Remis Auditorium at the Museum of Fine Arts in Boston on July 2, 2008. (Travis Dove for The Boston Globe)

Threatening skies forced Beth Orton's pair of concerts on Wednesday indoors from the Museum of Fine Arts' open-air Calderwood Courtyard - and it's probably a good thing. This stripped-down show was a study in pristine picking, thoughtful lyrics, and the quirky contours of a thoroughly original singing voice, and not a note or word was lost to the wind in the safe confines of Remis Auditorium.

It was the opening night of Orton's long-awaited tour following an 18-month maternity leave, and her first show with the stunning multi-instrumentalist Rob Moose, a member of Antony and the Johnsons. Orton chose well. The pair (she played guitar and piano; he played guitar, mandolin, and violin) seemed to share an inspired chemistry during an hourlong second set of finely built ballads and rambling midtempos spanning the artist's 12-year career.

Having steadily moved away from the ambient beats and delicate electronica that colored her early work, Orton has emerged as a full-blown descendant of the British folk tradition. She's also one of the most interesting vocalists working today, possessed of clear, quivering tones and oddly shaped phrases that tumble out like autumnal daydreams.

In this acoustic setting, nearly all the songs sounded untethered to time and place. From stately "Shadow of a Doubt" and rootsy "Countenance" to gently searching "Shopping Trolley" and bittersweet "Comfort of Strangers," Orton evoked the ageless beauty of Nick Drake and Sandy Denny.

A strapping woman in a loose dress and low boots, Orton the sober tunesmith shared the stage with Orton the daffy cut-up. One minute she'd be cursing and spewing gallows humor, the next swooping through elegant, aching "Central Reservation" or wrestling with the haunted melody on "She Cries Your Name."

"I'm going to try to make this one sound new, because to me it sounds like everything I'm playing tonight," Orton fretted near the end of the set, and she was right. For all the unique qualities of her songs, many of them share a common bone structure. There's a sameness to where her chords sit and how her melodies move, which is why Orton's performance of "Katie Cruel" - a traditional song she recorded for Bert Jansch's 2006 album, "The Black Swan" - felt so powerful. Released momentarily from her own well-trod patterns, Orton's familiar quiver morphed into passionate, almost confrontational, tones, and it was a welcome shift in color.

But lack of variety seems a small cost with an artist as consistently mesmerizing as Orton is. She closed the show with a trio of songs - "Sugar Boy," "Safe in Your Arms," and "Stolen Car" - all of them hovering in the sweet spot between tragic and triumphant, each one as lovely and bewitching as the next.

Joan Anderman can be reached at anderman@globe.com.