A milquetoast maniac holds three co-workers hostage over the Thanksgiving weekend--in a psycho-ordeal that begins crisply, with coolly ironic matter-of-factness, but soon slips into heavy-breathing, games-people-play melodrama: a veritable festival of implausible behavior. The increasingly unconvincing mini-terrorist here is Eugene Brackin, 46, sexually repressed product of a loveless foster-home childhood. And so, with no goal except getting some power and attention, Brackin--asked to come into work (marketing department, Felton Products, Ohio) on the day after Thanksgiving--arrives at the offices with supplies, padlocks the door, waves a gun, and makes prisoners of: smarmy boss Mr. Gaylord (whose wife is cheating on him); trim, proper secretary Mrs. Talmage, 62; and wise, sexy, ambitious colleague Sally Laird. These three try to talk Brackin out of his scheme, of course. So does--by phone--Deputy Police Chief Smolen, whose low-key approach soon gets him into squabbles with more trigger-happy officials. But Brackin, while insisting that he has no ""demands,"" remains adamant, with sporadic fits of violence flaring out of his usual courtliness. Sally, therefore, starts taking another tack: cooing admiration and alliance (""I think what you're doing here is extraordinary""). And after Brackin gets upset by Smolen's exasperated break-off in communications--""'They've left me alone. Oh, no. . . .' Brackin cried. He cried for forty years""--the captor and hostages get drunk together: Mrs. T. tells her life story (abortion, stifled ambitions) to Sally, later dances gaily; Sally lets out her hostility against the boss (threatening to castrate him) and completes her seduction of Brackin (""When she grabbed his penis he thrashed and thought he would explode as fear and ecstasy challenged his existence""). Finally, however, Sally--a murkily drawn quasi-feminist villain--uses this power over Brackin not to save everybody but to do in the boss. . . and there'll be two fatal shootings plus a near-fatal leap out the window by Mrs. T. (deranged by the ordeal). Minimal suspense, inconsistent characterizations, and no original touches--but here and there, especially in the opening pages, Gilbert shows a perhaps-promising feel for spare, dry, black-comic narration.