“She had the flu,” Perec said thickly. “They called Dr. Kiel—those people at the hospital couldn’t tell their right fingers from their right hand. They were always demanding his help. Anyway, he was the chief public-health officer for the county, even the state for a time. They called him in, and he cultured her blood, and he told them it was flu. It can kill someone, especially an older person, fast.”

“Flu. No matter what he saw under the microscope.”

She started to blaze up at me, but I interrupted. “Lucinda Ferring was his tech. She was in that lab. She was a black woman doing menial work, so she was invisible. I bet she knew everything you did and more besides, because you weren’t out on the shop floor with the students and Sonia, who worked as a lab dishwasher. If someone—was it Magda?—was bringing Y. pestis into the lab, even if Ms. Ferring didn’t know about it, she would have been exposed to it.”

“You’re trying to smear his name—”

“Did he give you a course of tetracycline about that time?” I cut across her again.

Her mouth opened in protest. Then came a horrified look, and she fell silent: memory had come back.

“He didn’t bother with poor Matt or Ms. Ferring. Not even his own daughter, not until she fell onto Matt’s dying body in that field.” Sonia had written about it in her journal—she was burning, thinking she was in a fire. Burning, freezing, attached to a respirator. The 1 percent who survived pneumonic plague, but neither parent welcoming the miracle.

“Kiel went to Washington to explain himself to the army. If he put the blame on his dead graduate student, it would reflect badly on him—why wasn’t he supervising his lab more closely? But the Czech bioweapons expert—what a lot of problems it would solve if she were responsible. What did he tell them? That he discovered she was a KGB agent, sent to steal U.S. germ secrets, that she actually conducted a trial diffusion for the KGB that killed a number of innocent people?”

“It was her fault,” Perec said fiercely. “He had proof, he showed it to the army, and they came and took her away to Washington. They offered her some kind of deal if she would work for them secretly at Fort Detrick. They gave her a new identity, Nathan told me, to hide her from the KGB. He said she wouldn’t be bothering us again.”

“And then she showed up here—when? a few weeks ago?—ready to blackmail Dr. Kiel, so she had to be disposed of, and how more artistically than with some of the pesky pestis that he’d kept locked away in a lab freezer all these years?”

“That’s a lie!” Perec jumped to her feet, spilling her tea across the table.