The demonic shriek and stampeding guitar that announce this 1970 watershed ("Immigrant Song") not only signals the group's first truly cooperative sound, it's also the bloodcurdling death scream of the relatively well-mannered '60s. No longer is Plant riding between mungo guitar riffs and "Moby Dick"-sized drums, and no longer do those ballsy sounds define the band's strengths. Deep in the LP, "That's the Way" and "Tangerine" prove that the quartet isn't good only for giving big sis the most gratifying night of her life -- they also offer convincing pillow talk the morning after.