When Massive Attack released its first album Blue Lines in 1991, the powers-that-be requested that the Bristol trio drop the "Attack" surname in light of the Gulf War. The action was fitting artistically as well, as "attack" isn't the word that best describes the pioneering trip-hop band's approach. "Massive" is more like it, especially considering the long list of musicians influenced or aided by Massive Attack: Portishead's Geoff Barrow, Tricky, producer Nellee Hooper (of Björk, Madonna, U2, and Soul II Soul fame), Neneh Cherry, and an uncountable number of new groups owe a large debt to Massive Attack's revolutionary merging of dub, reggae, hip-hop, soul, and ambient music. It's been four years since the band's Protection, and the stakes are high for the new Mezzanine: After all, as the progenitor of a genre, Massive Attack must hold its own against a legion of imitators just to save face. Fortunately, Mezzanine does just that. Enlisting the vocal support of Cocteau Twins' Elizabeth Fraser and reggae star Horace Andy, among others, Mezzanine is much darker than either of the group's previous offerings. Smooth without being slick and laid-back without being boring, tracks like "Teardrop" and "Group Four" may not be the stuff of bedroom revolution anymore, but nobody makes menacing mood music quite like Massive Attack. Only the awkward presence of a distorted guitar on a few tracks seems out of place, as overt aggression is generally anathema to Massive Attack's sound, but overall, Mezzanine is a welcome return and a new challenge to would-be contenders and copycats.