Light marks that fine writer M John Harrison's first return to the heartland of SF--including spaceships and hair-raising interstellar chases--since his apocalyptic anti-space opera The Centauri Device (1975). The heavy SF action begins in 2400. Space-going humanity is the latest of many civilizations to be baffled by the impenetrable Kefahuchi Tract; that vast stellar region where an unshield...