A so-so doomsday script about a collision between a minor asteroid and terra not-so firma, by the author of The Fire Came By (1976), a non-fiction account of the 1908 Tunguska disaster. Hermes is a mile-long chunk of solid nickel-iron, shaped like a primitive ax-blade and headed smack for the continental United States. Can it be safely blasted to smithereens beyond the limits of the atmosphere? No, given (a) the appalling condition of the decaying Air Force Minutemen in their silos and (b) the paranoid-schizophrenic collapse of the astronaut in charge of planting a hydrogen bomb on the thing after the Air Force failure. Sci-fi fans will find the astronomical material rather thin and arbitrary; Baxter never so much as tries to indicate Hermes' path relative to the ecliptic. This is really for the disaster clientele: lots of snappily choreographed tidal waves, superhurricanes, hydrophobic generals, smeary sex, and cheery violence. Baxter does it all well enough to make one wish he'd do something better.