First, Robert Plant regained his shamanistic rock muse on the global-tripping Mighty Rearranger. Then he cut Raising Sand, a sublime duets set with Alison Krauss. Here, Plant takes a dark detour with Patty Griffin and guitarist Buddy Miller. This covers set is many shades of swamp noir, with songs by Townes Van Zandt, Richard Thompson, indie slowcore specialists Low and obscure R&B rockers. The results are deep, moving and brooding, with a sense of dread seeping into even the most joyous songs. Still taking notes on American music, Robert Plant reflects something very jarring back at us.