In a first hardcover medical-thriller, Goldberg (a clinical professor at UCLA Medical Center) gives HMOs rough treatment while concocting a scalpel-edged page-turner. Heroine Dr. Joanna Blalock, a Los Angeles pathologist (also featured in the earlier paperbacks Deadly Medicine and A Deadly Practice), is back at Memorial Hospital, where a recent outcropping of Legionnaires' disease had flooded her dissecting rooms with an overflow of coroner's cases. Suddenly three more appear: two bone- marrow transplants and one breast cancer--the bodies of patients who died unexpectedly of unknown causes just as they entered Memorial for treatment. Even though her dissections, resections, and cell and blood analyses draw blanks, Joanna smells murder. Meanwhile, readers will find E.R.'s visuals light stuff beside Goldberg's knowing corpse-cutting, popping out of inner organs, and poison-seeking. We are also well aware that a monster is loose in the form of Karl Rimer, a Vietnam-trained assassin who now works for the Agency--and does outside jobs as well, as he is doing in L.A. Joanna's affair with homicide detective Jake Sinclair is fading badly, even though their paths cross often in the investigation. Slowly, the reader, if not the two leads, comes to suspect that Health First, an HMO that sent these three failing patients to Memorial, is somehow behind the murders. The burgeoning Health First is masterminded by Dr. Robert Mariner, a now middle- aged boy genius reminiscent of Jonathan Winters's cemetery owner in The Loved One, who complains, ``What are all these stiffs doing on my property?'' When Joanna gets too close to the truth, Rimer sets out to remove her, forcing her car over a cliff. Joanna survives, though, an amnesiac pursued by a murderer when she doesn't even know who she is. . . . Cool cuttings by a sure hand.