When they're firing on all cylinders (as on past albums The New Farming Scene and Pencaitland), there's no better balance of American bluegrass pizzazz and Celtic folk harmonies than the patented brand knocked out by Southern Tenant Folk Union.

The pace slowed on 2013's Hello Cold Goodbye Sun, as the Edinburgh-based band blew a prog-rock haar across songs that typically champion the working man. And now, pushing their art a fair bit further, they're filtering a succession of measured minor chords through arrangements that, in terms of ambition, look to a hybrid of Kronos Quartet and Punch Brothers.

None of which sounds like the result of a concept album where every song references a Chuck Norris movie. It's not, of course, a concept album in the strict sense, as this particular actor's conservative politics and action-fuelled output could never chime with observant lyrics and delicate musical moods like these. Instead, the titles form a launchpad for songs that lie much closer to STFU's ever-evolving heartland.