Readers who eagerly pick up this new computer-thriller by the savvy author of The Consultant and Spy Game will probably be engrossed at first, then slightly skeptical . . . and ultimately disappointed (or even actively annoyed). The novel's first half is engaging, involving, enormously promising: Toby Sorenson, security chief for a Massachusetts computer company (where there's been a puzzling theft), is going through a rocky reunion with his ex-wife Elaine and their ten-year-old son Jay--who is manically obsessed with a home computer called the ""Possum""; meanwhile, a local CIA clerk (a Russian Ã‰migrÃ‰) claims to have spotted a hated KGB officer from bygone Siberia days. . . on Beacon Hill! How will these two plot-lines be linked up? That's the initial grabber here--while McNeil does a charming job with the ex-spouse/prodigal-father situation; and the tension remains strong when, dragged to a home-computer exhibition by Jay, Toby begins to suspect that the Possum manufacturer may have been involved in that theft from Toby's own company. (With help from Jay, Toby does a neat--if unilluminating--little break-in at the Possum plant.) Then, however, the plot starts leaping from life-sized intrigue to sci-fi-ish melodrama--as Jay, deprived of his Possum (punishment for playing hooky), near-fatally attempts suicide: the distraught Toby now hooks up with the CIA, trying to convince them that the Possum computers are programming kids into bizarre behavior with subliminal messages. And, since there are several other cases like Jay's, the CIA seems to take Toby seriously, with growing suspicion that the Possum mastermind is none other than that one-time KGB officer. But when the CIA suddenly abandons the case, Toby gets the paranoiac feeling of a somewhat broader sort of conspiracy, a feeling that's confirmed when he learns the spooky life-history of that KGB man. So, finally: is some Bigger Force behind the computer-brainwashing of American kids?! Fans of third-kind encounters (or pods) may welcome this surprise/cop-out windup. Admirers of McNeil's previous books, on the other hand, are likely to feel cheated--especially after having been drawn in so effectively by the character-appeal and computer-fascination in the novel's splendid first half.