The embrace of Arthurian legend and Tolkien-esque fantasy by British musicians in the 1960s and 70s — fueled undoubtedly by mixing the sounds of the folk revival with psychedelics and horrified revulsion at an overly industrialized and de-personalized world — worked to create some truly exotic hybrids in a scene that had also been profoundly influenced by American blues music and the sheer power of electric instrumentation. But whether it was Donovan or Led Zeppelin or Uriah Heep taking on the Roundtable and Middle Earth, there tended to hang over this music a hippie haze that could just as easily turn towards the naively dumb as the innovative. (Spinal Tap’s “Stonehenge” sequence is funny because it’s so spot-on, and as a Zep and Rainbow fan I laugh, and squirm, whenever I see it.) Leave it to Pentangle to get it right. As Bert Jansch introduces “Hunting Song” as a “13th-century rock and roll song” on this stellar performance from the band’s 1970 BBC special, his is a voice of wry authority. A key figure in the development of acoustic guitar playing in the 1960s, and a songwriter who found inspiration in the dark power of traditional music, Jansch was a musician who masterfully summed the denominators of blues and jazz and folk music early in his career, and until his death in 2011 was a guitarist’s guitar player. While Pentangle could not be said to be Jansch’s band, as it also included a cast of equals including guitarist John Renbourn, bassist Danny Thompson, drummer Terry Cox and vocalist Jacqui McShee, they built on the ground Jansch cleared in the mid 1960s along with Martin Carthy and John Fahey. Their music is jazz medieval, folk improv, well-suited to covering one genre’s songs with another’s genre’s music. “Hunting Song,” originally recorded in the studio for 1969’s Basket of Light, adapts, from the Arthurian take on Tristan and Isolde, the story of Morgan Le Fay’s magic drinking horn, which revealed faithlessness in those who were incapable of drinking from it. The narrator’s role in the story isn’t entirely clear, and the broken narrative itself is, in a moment of genius, written as if the band found it on a shard of manuscript. There is a hunt, a horn, a betrayal. The sources are uncertain, our interpretations our own. Here we see a rare moment of electric guitar work from Renbourn, and Thompson, as always central to the Pentangle sound, hunched over his upright bass, working with Cox to both support and lead the tune. Although Jacqui McShee didn’t possess the vocal firepower of Maddy Prior or Sandy Denny, she matched them in finesse, and beautifully floats over Jansch’s rougher, Dylanesque delivery. As a crossroads of jazz, progressive, and traditional music, this is one of British folk-rock’s great moments.