When Bloc Party went on a lengthy hiatus after the release of their third album Intimacy, it didn't seem like they needed to get back together. The band's members had moved on, with Kele Okereke releasing his solo album The Boxer and bassist Gordon Moakes forming the group Young Legionnaire. More importantly, it seemed like Bloc Party had said its piece, but Four -- an album title that reflects the years between the band's albums, the number of its members, and its place in Bloc Party's discography -- shows there's more life in their music than most would have predicted. The bands from the post-punk/angular movement of the early 2000s that thrived were the ones who evolved; Bloc Party knew this as early as A Weekend in the City, when they began adding more electronic elements to their sound. This led to some strong moments on that album and Intimacy, but it also felt somewhat obligatory, following the Radiohead-blueprint way for a forward-thinking rock band to push itself. Yet Bloc Party push harder on these songs than they have in years, and there's barely a synthesizer or sequencer to be found. Four is far harder-edged than any of their music since Silent Alarm or their early EPs, and they spend equal time in familiar territory and breaking new ground. "So He Begins to Lie," with its lumbering, angular riffs and political overtones, could have easily appeared on their debut, while "V.A.L.I.S." and the excellent single "Octopus" distill everything great about their pop side -- precise melodies, spring-loaded guitars, expertly deployed tension and release -- into songs that seem poised for flight. Meanwhile, ballads such as "Day Four" and "Truth" are pretty but a touch predictable, serving more as breathers between the album's onslaughts than as attractions in their own right. Four's real star is guitarist Russell Lissack, who unleashes hesher-friendly riffs and solos with the pent-up fury of a four-year break behind him. He gives "Team A"'s menacing dance-punk extra heft and fuels "3 x 3"'s anguished tug-of-war with churning riffs that make it one of the album's most thrilling moments. Things get even gnarlier on "Kettling," which boasts surging riffs that recall P.O.D. and other X Games favorites, and on "Coliseum," which begins as a bluesy shuffle and ends as a metallic grind that would do Helmet proud. It's awkward, but it's also interesting and completely unlike anything they've done before. Songs like this and the album's closing rant "We're Not Good People" show just how much fight there is in this album, and in Bloc Party; they sought new life in their music and their collaboration, and they found it. Four may not be as cohesive as Silent Alarm, but it just might be more vital.