Ringworld Engineers

Ringworld (1970), the most celebrated work in Niven's Known Space sequence, posited a vast body of matter - enough for an entire solar system - spinning around a sun in the form of a single giant artifact of unknown origin: a continuous million-mile-wide ribbon provided with oceans, atmosphere, and vast flat projections (life-size maps ) of Earth and other inhabited planets. The present book takes up the puzzle some 20 years after Louis Wu's escape from the Ringworld. Kidnapped by the mate of Nessus, their two-headed alien companion of the previous voyage, Louis and his catlike ally Chmeee are transported to the Ringworld - now spinning dangerously off-center - in an attempt to discover the cause of the aberrant rotation before the world grazes its sun. Searching for clues to the design of the structure's long-vanished original engineers, they encounter various hominid and other races before finding the barely feasible, wholly appalling solution hidden beneath the Map of Mars. Niven, a longstanding favorite with hard sf buffs, commands an impressive vein of invention, but his plotting here is limp and threadbare; the idea was more striking the first time around. (Kirkus Reviews)