Kicking off the band's 1970-released third album, "Immigrant Song" is Led Zeppelin at their most powerful and basic, riding an up-tempo groove and a stomping Jimmy Page guitar riff that simply switches between two octaves of the same note. As the song opens, John Bonham's drums double the riff, and Robert Plant's otherworldly howl enters shortly thereafter, singing a piercing, wordless melody that seems to invoke the spirits of the long-dead mariners mentioned in the lyrics. The "immigrants" of the title are actually ancient Viking conquerors (there are references to "the land of the ice and snow," "the hammer of the gods," and Valhalla), and the unearthly quality of Plant's voice helps establish an aura of mystery and pagan myth about the song that makes it as eerie as it is hard-rocking. Plant also projects a certain menace in keeping with the warlike nature of the song's characters, and his softer, slinkier tone on threats like "We are your overlords" contrasts nicely with the shrieking chorus. Although "Immigrant Song" isn't too technically challenging, there are quite a few change-ups from the main riff that keep things from getting repetitive; there's also an unorthodox ending which uses a melody and variation on the main riff not heard previously in the song. While the rest of the band plays well, "Immigrant Song" is really Plant's showcase, and he turns in a stellar performance.