The Civil Wars, the duo of Joy Williams and John Paul White, met in Nashville a couple of years ago. They tried writing songs together, and things happened very fast. Their song “Poison & Wine” ended up on a Grey’s Anatomy episode; they recorded a couple of EPs that got noticed (Taylor Swift mentioned them in a tweet); they appeared on The Tonight Show, All Things Considered, and A Prairie Home Companion; and their debut full-length album, Barton Hollow, hit the Billboard top fifteen. Here in town they sold out the Ark last spring and are back for a return engagement at the Michigan Theater on November 2.

“Poison & Wine” was a terrific song, with complexities unfolding in multiple dimensions from its opening line, White’s “You only know what I want you to.” “I know everything you don’t want me to,” Williams answers, and a couple’s mix of connectedness and tension is explored not only in the lyrics but in the two singers’ harmonies, seductive yet full of daring clashes. The song fades out on the contradictory line “I don’t love you, but I always will,” sung by both together. The Civil Wars have recorded “Poison & Wine” twice and re-created it in different forms several more times, filling out their albums with straight love songs and a few numbers on topics other than the labyrinth of love.

These two musicians are, they say, creative but not romantic partners (Williams, at least, is married to someone else). Plainly they’ve gotten good mileage out of the inherent tension between their seeming emotional intimacy and their unattached status, and you wonder where they can take it from here. For the present, though, the music is sparse (often accompanied by just one guitar) and often electrifying. Lots of people are singing harmony in the acoustic music field these days, but it’s rare, and commands respect, when two singers come along who seem to be able to read each other’s minds and produce daring combinations.

Beyond the ideas and the harmonies, the Civil Wars sweat the small details and get a lot out of a very few sonic elements. The engineering of their recordings results in startling vocal detail, and their live show should be one of the few in which performers, emotionally and technically, draw listeners into a closed, intimate world. The Civil Wars are the hot act in folk music for the moment, for good reason.