Larry Brokaw, president of California's Northridge Electronics, decides it's time to diversify--into defense contracts--so systems-designer Martin Avery is dispatched to England to study ""Vulcan"": a system for computerized war games which Brokaw intends to buy outright from Quantek Electronics and market to the Pentagon. And, indeed, Avery is very impressed by his first visits to Quantek's offices and to the Royal Armaments Research and Development Establishment at Fort Halstead--where the British stage elaborate mock-WW III scenarios using a Vulcan system bought from Quantek. But soon he has reasons to be suspicious: a Fort Halstead aide named Franklin has disappeared; one of Quantek's partners, boozy Pat Corrigan, is acting oddly (Avery realizes he saw Franklin together with Corrigan just before the disappearance!); and British Intelligence is chasing about. So it looks as if Corrigan and Franklin have been up to some traitorous spying--especially when Corrigan ends up dead in a car ""accident."" But when good-citizen Avery clues in U.S. Intelligence, he's told to mind his own business. And then, sleuthing on his own with help from Corrigan's sexy secretary, Avery closes in on the real explanation: Franklin, whose apparent defection was obviously faked, had caught on to a pattern of computer breakdowns at Fort Halstead--breakdowns which then required servicing. . . which made it possible for a data-stealing minicomputer to be installed in (and later removed from) the war-games computer system full of military secrets. This is a neat twist, as is its direct connection to Avery's original assignment. And McNeil's generally wry, downbeat style and offbeat characterizations add much-needed human texture to the technical trickiness. So, though Avery's dogged heroics here are a bit implausible--and though the sleuthing sometimes becomes long-windedly routine--this is a worthy follow-up to McNeil's even better, more distinctive computer-suspense debut, The Consultant (1978).