Call him a crusader. Robin Cook writes his thrillers not so much to entertain, but, as he once said in an interview, to "alert the public to medical dangers, to get them interested in an issue before it develops into a catastrophe."

Trained as a physician at Columbia and Harvard universities, the best-selling author made his debut 30 years ago with "Coma," which went on to become a Michael Crichton-directed movie.

Ever since, he has been churning out medical thrillers one after another, exploring such issues as managed healthcare, stem cell research, organ transplants, bioterrorism, genetic engineering and cloning.

Some subject matter is not conducive to dramatization, and last year's "Crisis," which dealt with doctors who lavish care on the rich for a retainer, made a pretty boring read. Luckily for his fans, Cook's latest effort, "Critical," is a top-notch thriller with the freshness and impact of his earlier efforts.

In the novel, the author combines two issues of growing public concern.

First, there is a bacterium that has lurked in hospitals for decades but now appears to be poised to burst on an unsuspecting public. Called Methicillin-resistant Staphylococcus aureus or MRSA, it kills the victim in a matter of hours.

The second issue has to do with doctor-owned, and some say profit-driven, specialty hospitals that offer specific services such as orthopedic surgery. Unlike regular, full-service hospitals, they lack the ER or ICU, so patients who develop postoperative complications could be in trouble. Given such scary material, the story practically writes itself.

ABOUT THE STORY

The potential victim is Jack Stapleton, a forensic pathologist in New York City's Chief Medical Examiner's Office. He injures his knee playing basketball and makes an appointment for surgery at one of the specialty hospitals owned by Angels Healthcare, a company about to go public and expected to make millions.

Laurie Montgomery, his colleague and new wife, becomes concerned about his safety when she dissects the corpse of a man who died of a MRSA infection after undergoing the same procedure Jack is planning to have and at the same hospital. Her anxiety deepens when she discovers that there have been more than 20 MRSA deaths — all at Angels Healthcare hospitals.

To find out what is going on, Laurie studies the victims' hospital records, examines specimens, consults with experts, and even searches Google for possible clues. "Critical" offers a genuinely titillating epidemiological puzzle, giving readers an opportunity to participate in Laurie's investigation vicariously, forming and discarding theories as to the outbreak's cause.

Jack and Laurie, who have appeared in Cook's previous novels, are not exactly charismatic characters, but because of their profession, they make ideal vehicles for Cook's campaign to raise public consciousness about medicine's pitfalls.

"Critical" is tightly written, and each supporting character is vivid and memorable. The novel is a credit to the medical thriller genre, which Cook is generally thought to have created and made popular.