Eleven years following their self-titled second album, Portishead’s Third is an inventive, challenging song cycle that never settles for easy listening. The time off was no vacation. Principal producer and writer Geoff Barrow was decidedly unhappy over the group’s comfort zone, disturbed that the ensemble’s experimental ways were so easily co-opted by others and fitted as a lifestyle soundtrack for a sophisticated, affluent class. With Third, the challenge was on to reinvent the group’s spooky trip-hop, film-noir magic as something far more extreme. “Magic Doors” and “Plastic” both clock in at the conventional three-and-a-half minute mark, yet in their compact structures the tunes cut-up and break down in unexpected jolts with beats slowed to crawls and Beth Gibbons’ eerie vocals tortured into free-fall. The minute and a half of “Deep Water” is a shockingly tame ukulele ballad with a barbershop quartet mocking Gibbons’ depressive observations, but elsewhere the emphasis is pure tension. The disruptive grooves of “Silence” set the ominous path. Songs shut down abruptly, or clang on with battered electronics (“Machine Gun”). Intense.