Unit 731 was an actual biological warfare research laboratory constructed by the Japanese at Ping Fan in Manchuria in 1939. At least twelve different organisms were studied there for their weapons potential, including plague, glanders, anthrax, and typhus. The facility covered six square kilometers and was as large as the concentration camp Auschwitz-Burkenau. Extensive human testing took place at Unit 731, as horrible as anything conducted by the Nazis in Germany. Anda Proving Ground actually existed, and outdoor tests on prisoners tied to stakes were conducted exactly as described.

The perpetrators of Unit 731 were never prosecuted. They were granted immunity in exchange for the results of their research. The Allies wanted to prevent this information from  falling into Soviet hands at the start of the Cold War.

A flea-infested plague bomb was developed at Unit 731 in June of 1941. It was actually scheduled for use against the city of San Diego in September of 1945, but the war ended just six weeks earlier.

The village of Congshan is a real village, and a test of a bubonic plague weapon was conducted there in August of 1942 exactly as described. As a result, 392 of the 1200 residents perished from plague over the next two months. At its peak, the plague killed twenty villagers each day.

Vivisections were a common part of the human experiments, because researchers wanted to study the effects of different pathogens before the body began to decompose.

The opening chapter of the book is based on a real story. In March of 1999, a man named Chua Kaw Bing needed to transport a sample of the deadly Nipah virus from Malaysia to the CDC in Fort Collins, Colorado. No courier would agree to transport the substance, so Chua packed it up and carried it himself on a commercial airline.

Because bubonic plague resides in rodent populations, it can never be eradicated. There have been three great plague pandemics throughout history, claiming the lives of an estimated 200 million people. There are 10-15 cases of bubonic plague in the United States each year. There is currently no vaccine against plague. Plague is listed by the CDC as one of its "Critical Biological Agents."

Over a twenty year period beginning in 1972, the Soviet Union conducted extensive research on biological weapons in general and plague in particular. In the city of Kirov, twenty tons of plague were maintained in their arsenals every year. Soviet scientists discovered ways to splice toxins into the plague bacterium, making it far more deadly than it is in its natural state.

When the Soviet Union collapsed in 1991, many Soviet bioweapons scientists were forced to look for work in other fields. Many left the country. Some disappeared.

The character of Pasha Mirovik is loosely based on a real figure, Kanatjan Alibekov. Alibekov was Chief Deputy Director of Biopreparat, the Soviet Union's bioweapons program, until 1992 when he defected to the United States and gave U.S. authorities their first comprehensive picture of the Soviets' weapons program. Alibekov holds two PhDs, one for research and development of plague and tularemia as biological weapons.