Cook, who has carved out a niche for himself with his charmingly whimsical spy capers (Paper Chase, Disorderly Elements), now stretches thin an oft-used premise-the HAL-like computer gone amok--in this tale of FATS, the first ""fully autonomous tactical satellite."" Up there in the sky, spying on the world, FATS overhears the President joke that we are at war with Russia and sets about destroying Soviet space-stations, etc. Nothing deters FATS from its mission; in fact, it views orders to abort as originating from the enemy. Thus, the hunt is on for Clem, the man who designed FATS and the only person who can maybe make it stop. But Clem has quit his defense work in a fit of despondency and has joined the homeless wandering the streets of London. Meanwhile, an assassin is dogging his footsteps. Will Clem be found before he's killed? Will he be able to reason with his brainchild FATS? Clem averts Doomsday, but not by much, and not before Cook takes his pokes at impetuous generals, warmongers, wacko politicians, and inane gamesmanship played by scientists, appropriations committees, and so on. Slight, but tart and amusing.