In his disjointed bestseller The Hot Zone, Richard Preston projected a gruesome Ebola epidemic spawned from infected laboratory macaques brought to the United States. At the time, Preston—with a reporter’s pumped-up copy—arguably fearmongered bioterror. Scientifically tempered minds claimed that an Ebola outbreak would have been easily contained, if one had ever occurred.

But cooler, conventional heads prevailed only before the anthrax attacks of 2001. Bioterror is now chillingly real. In his new, sleeker book, The Demon in the Freezer, Preston segues neatly from the genuine tragedy of the anthrax assault to the possible, deliberate spread of the highly contagious and deadly smallpox virus. This time, Preston explores a threat befitting his heated prose.

A once uncontrollable, tormenting disease affecting only humans, smallpox was officially wiped off the planet in 1980, thanks to the extraordinary vaccination effort of the World Health Organization. With the infection’s extinction, WHO urged that civilians worldwide no longer be inoculated: Risks of the vaccine’s rare, but serious, adverse effects—including death—outweighed the minuscule odds of a natural recurrence. The only sanctioned repositories for the virus are in the United States (at the Centers for Disease Control and Prevention in Atlanta, Georgia) and in Russia. But bioterror experts believe that rogue stocks must exist—including, Preston indicates, unaccounted tons of secretly cultured virus in the former Soviet Union. And these supplies may be within reach of the perniciously inclined.

With aptly grim verbiage, Preston captures the closing wreckage of smallpox, a disease long forgotten or entirely unknown to most. He describes the seminal case of a small, hospital-based outbreak in 1970 Germany: “The inside of his mouth and ear canals and sinuses had pustulated, and the lining of the rectum may also have pustulated, as it will do in severe cases, yet his mind was clear. When he coughed or tried to move, it felt as if his skin were pulling off his body, that it would split or rupture.” The same virus found its way to a student nurse, who had had no contact with the initial victim: “The skin became rubbery and silky smooth to the touch, with a velvety, corrugated look…The whites of her eyes developed red spots, and her face swelled up as it darkened, and blood began to drip from her nose.”

Smallpox is the supreme bioterror threat, because the disease is so agonizing, easily transmissible, and ultimately lethal. Unlike anthrax, smallpox is readily caught from an infected person through the air, for instance, through a ventilation system; direct contact is unnecessary. In those persons vaccinated decades ago, immunity is vanished. If unleashed in today’s mobile world, smallpox could overwhelm humankind in an excruciating way. In Demon, Preston grasps the contemporary menace of smallpox, without hyperbole.

Preston lays out a history of smallpox—its putative evolution and subsequent eradication through the colossal WHO effort—and a background of Biopreparat, the massive, covert biowarfare program in the former Soviet Union. These respective subjects were more comprehensively and knowingly mined by bioweapons expert Jonathan B. Tucker in Scourge: The Once and Future Threat of Smallpox (2001) and by former Biopreparat director and defector Ken Alibek in his memoir Biohazard (2000). But unlike these authors, Preston can avail of the new world order, after 9/11 and the anthrax terror: The urgency to safeguard civilization is now acutely felt.

And revealed within this new-world context is the pressing need for vaccine stockpiling, long advocated by senior government virologist Peter Jahrling. (Jahrling initially feared that the mailed anthrax spores were laced with smallpox. They weren’t.) Preston reveals a running conflict between the likes of Jahrling and D. A. Henderson, former director of the WHO vaccination program and current head of the newly created Office of Public Health Preparedness. Jahrling advocates experimentation with smallpox to develop an antiviral agent for those unable to receive the vaccine (for example, the HIV infected). In 2001, Jahrling directed a series of unprecedented and controversial smallpox infections in laboratory monkeys.

Henderson, conversely, has long promoted the destruction of the smallpox repositories, primarily as a global example of intolerance to harboring the pathogen. To investigators like Henderson, Jahrling’s animal experimentation with smallpox is largely futile and a step in a morally wrong direction. Al Sommer, former WHO field worker and current dean of the Johns Hopkins School of Public Health, believes that Jahrling’s work pushes other countries to conduct their own smallpox experiments. Preston quotes Sommer: “We could start an arms race over smallpox…”

The most disturbing event revealed in Demon is the creation by Australian scientists of a genetically engineered mousepox virus (the smallpox equivalent in mice) to which innately mousepox-resistant rodents are highly susceptible. This development suggests that bioweaponeers could develop or have already constructed a smallpox supervirus that renders the current vaccine wholly useless.

Preston warns, “The main thing that stands between the human species and the creation of a supervirus is a sense of responsibility among individual biologists…The international community of physicists came of age in a burst of light over the sand of Trinity in New Mexico. The biologists have not yet experienced their Trinity.” With Demon, Preston warns to brace for it.