Shannon McArdle has one those amazingly nuanced countenances: a sly smile that amplifies her natural beauty but depending on the light and the mood can seem either playful or pained—or both. You don’t know whether she’s chuckling or whether you’ve touched a nerve. You see it in photographs, but when she’s live and on stage, it’s magnified that much more.

If you were among the modest, but enthusiastic audience gathered for her CD release party at the Mercury Lounge, and didn’t know any better, you wouldn’t have immediately pegged her for someone who’d just put out an album of such wrenching, tough-minded confessionals. She was in a cheerful, ribbing mood during her 45-minute set, and even the most doleful songs from her new Summer of the Whore were rendered with a certain sprightliness—she’s glad to be out and airing this material live after spending so many apparently brutal, soul searching hours realizing it.

McArdle isn’t entirely ready to leave her past behind, at least musically, and understanding the drama on Summer means a crash course in the Mendoza Line, the critically adored and criminally underappreciated alt-country band in which she co-starred for seven of its eleven years of existence. She joined singer/guitarist Timothy Bracy in Mendoza in 2000 and established herself as one of the group’s principal songwriters. McArdle and Bracy also released an album as a duo under the name Slow Dazzle and got married in 2005, all in the midst of their Mendoza releases picking up a small but significantly devoted fan base (including rock critic paterfamilias Greil Marcus) along the way. It was a good run, and it crashed and burned two years later as the marriage broke down and the Mendoza Line’s 30 Year Low—one of the best and most brutal albums of 2007—arrived as an epilogue, swathed in bitterness and as potent a combination breakdown/breakup/breakdown again album—as has been noted on several occasions—as Richard and Linda Thompson’s Shoot Out the Lights.

We’ve heard little from Bracy since Mendoza’s demise; he gigged a bit with Timothy Bracy’s Collection Agency, which contained a few Mendoza alumni and was listed on its SXSW dossier as being from McLean, VA, but whose MySpace page has since vanished. So, it’s McArdle who gets the official, first-out-of-the-gate honors since the dissolution. She’s not the only Mendoza Line alumnus in the band—drummer/guitarist Adam D. Gold helped her record much of the songs—and at the Mercury she filled out her sound with a bassist, electric lead guitarist, and fiddler.

It’s the latter instrument that strikes a faint measure of familiarity. Every time you’re convinced McArdle’s left the Mendoza strain behind for something that grabs hold of Liz Phair- or PJ Harvey-style brusqueness in one hand and the Velvet Underground in the other, a string creeps in, a countrified guitar lick pokes out, or a mournful lyrical passage is there to stake McArdle, however peripherally, in alt-country.

Sure, there’s enough variety to broaden her sound—“Leave Me For Dead” is fitful garage rock in the midst of all the slower stuff—but the best songs both live and on record are twisted country songs: the dark “He Was Gone”, about what potential (i.e. a baby) is lost by a broken marriage, and the darker “That Night in June”, whose cold, creepy undertones recall the Willard Grant Conspiracy and similar mavens of dread. They make other selections like the more pop-inflected “This Longing”—“I sit by the phone like a thirteen year old / Convinced that you’ve already called”—seem like underwritten toss-offs, especially when McArdle is elsewhere willing to be so frank and loaded (as in the title track and “Poison My Cup”), puncturing her verses with “Just fuck me up” and similarly profane conversation-stoppers.

Overall, the songs need more time to marinate, and the Mercury’s phlegm-y sound mix drowned the vocals and any other small details in a too-pronounced guitar crunch and a leaden bottom end. But McArdle’s frank confidence and complementary sound—one that incorporates just enough of her former band to feel familiar—means she’s thrown her hat back into the ring: thus far, all the post-Mendoza spoils are hers.