Presumably inspired by actual recent cases of pet monkeys offering crucial life-support to quadriplegics, British novelist Stewart offers a crisp, half-fanciful concoction--which moves, not quite convincingly, from documentary-like case history to ESP-ish, psycho-pharmaceutical suspense. Oxford law student Allan Mann is an obsessive runner with Olympics plans. . . till, after a fight with actress-girlfriend Linda, he wrecks his motorcycle and--despite surgery by Dr. John Wiseman--winds up paralyzed from the neck down. Back in his apartment, tended by a nurse and his newly-widowed mother, Allan is helpless, angry, understandably depressed, failing in a suicide attempt. But then, hoping to provide Allan with the essential function of a human brain (""a body to control""), his friend Geoffrey, psycho-pharmacology expert at the Department of Experimental Medicine, gives the wheelchair-bound man a pet/trainee: Ella, a Capuchin monkey from the experimental lab. And, indeed, as Ella slowly learns (via behavioral techniques) to help Allan with daily tasks, Allan rediscovers life--intensely returning to his law studies, becoming emotionally attached to Ella. Furthermore, Ella seems to be responding remarkably to Geoffrey's latest drug-experiment: an intelligence-boosting pill that's supposed ""to stimulate the uncommitted cortex in such a way as to make it more receptive to assimilating new codes of cell-firing patterns."" (Allan, hoping to enhance his law-studying, also swallows the pills.) Then, however, the novel starts taking less persuasive, more standard-horror-fiction turns--as Allan becomes obsessed with wreaking vengeance on surgeon Wiseman, who just happens to be marrying old-flame Linda. And when John and Linda are critically burned in a fire at their cottage, Allan (who had a fiery dream that night) soon realizes, along with Geoffrey, that Ella is the culprit: those brain-pills, it seems, have also created super-ESP between Allan and Ella--making her a ruthless killer who does Allan's unspoken bidding! So there'll be more deaths, with Allah's painful dilemma (""How could he stop her if she was an extension of him?""), before the violent-yet-upbeat ending. Uneven in tone, with neither the sparkle of Michael Crichton nor the involving seriousness of, say, Richard Setlowe's The Experiment--but a lively, often intriguing smorgasbord of medical-ordeal, neuro-science, paranormal chills, and man/animal love-story.