Sequel to British fantasy writer Lumley’s hybrid sf/games fantasy The House of Doors (1990, not reviewed) in which alien Thones try to take over the Earth. The Thones’s original House of Doors was a gamesmaster’s torture chamber built to test the adaptability and intelligence of native species. When a small group of earthlings, led by Spencer Gill, defeated the House of Doors, the aliens acknowledged our smarts and, going by their own moral code, departed, granting our right to survive. Now they’re back--or a renegade group is--and set on using Earth as a breeding ground. First to notice them is a fisherman in Shantung Province who finds that a hundred-foot-tall, doorless and windowless pagoda has suddenly appeared on the shore below his house in the brief moment it took for him to put on his hat. Rowing out to the pagoda, he finds that it’s a kind of virtual-reality structure that shimmers, although he can step onto its steps--well, momentarily, until a terrific suction within the pagoda frightens him into leaping back into the sea. Meantime, in Egypt a doorless pyramid appears, while in the ocean a large iceberg has become stationary. In England, “Machine Man” Spencer Gill is again called in, this time to study some simultaneous glitches in the world’s radio telescopes. Gill himself represents a quantum leap in human intelligence, since he understands computers and all machines by touch, taste, smell, sight, and listening to and feeling for them. The telescope glitches are eight spatial anomalies--holes in space!—that equidistantly form a cube around the globe. Then all the oceans start to clog with massive outbreaks of algae, which is what the Thones plan to use to suffocate the human population. But first they must capture Gill and his party in a House of Doors. More straightforward than Lumley’s Necroscope series, and fun on a heroic sf level.