Then his eyes focused on two unfamiliar envelopes. One was a large manila envelope, the other was business size. Jack opened the manila one first. It contained the copy of a hospital chart. There was also a note from Bart Arnold saying that he’d taken it upon himself to get a copy of Kevin Carpenter’s chart to add to the others Jack had requested.

Jack was pleased and impressed. Such initiative was commendable and spoke well for the entire PA investigative team. Jack opened the chart and glanced through it. Kevin had been admitted for an ACL repair of the right knee, which had gone smoothly Monday morning.

Jack stopped reading and thought about the fact that Kevin had been immediately postoperative when he’d come down with his symptoms. Putting Kevin’s chart aside, he picked up Susanne Hard’s and confirmed that she, too, had been immediately post-op, having had a cesarean section. Looking at Pacini’s, he confirmed the same.

Jack wondered if having had surgery had anything to do with their having contracted their respective illnesses. It didn’t seem probable, since neither Nodelman nor Lagenthorpe had undergone surgery. Even so, Jack thought he’d keep the operative connection in mind.

Going back to Kevin’s chart, Jack learned that the flu symptoms started abruptly at six P.M. and progressed steadily and relentlessly until a little after nine. At that time they were considered worrisome enough to warrant transferring the patient to the intensive-care unit. In the unit he developed the respiratory distress syndrome that ultimately led to his death.

Jack closed the chart and put it on the stack with the others. Opening the smaller envelope-addressed simply to “Dr. Stapleton”-Jack found a computer printout and a Post-it note from Kathy McBane. The note simply thanked him again for his attention to the affairs of the General. In a short postscript Kathy added that she hoped the enclosed printout would help him.

Jack opened the printout. It was a copy of everything that had been sent from central supply to a patient by the name of Broderick Humphrey. The man’s diagnosis wasn’t mentioned, but his age was: forty-eight.

The list was just as long as the lists he had for the infectious disease index cases. Like the other lists, it appeared to be random. It was not in alphabetical order, nor were similar products or equipment lumped together. Jack guessed the list was generated in the sequence the items were ordered. That idea was bolstered by the fact that all five lists started out identically, presumably because as each patient was admitted, he required standard, routine equipment.

The random nature of the lists made them hard to compare. Jack’s interest was finding any ways that the control list differed from the others. After spending fifteen wasted minutes going back and forth among the lists, Jack decided to use the computer.

The first thing he did was create separate files for each patient. Into each file he copied each list. Since he was hardly the world’s best typist, this activity took him a considerable amount of time.

Several hours drifted by. In the middle of the transcription process Laurie again knocked on his door to say good night and to see if she could do anything for him. Jack was preoccupied, but he assured her that he was fine.

When all the data were entered, Jack asked the computer to list the ways the infectious cases differed from the control case. What he got was disheartening: another long list! Looking at it, he realized the problem. In contrast to the control case, all five infectious cases had had sojourns in the intensive-care unit. In addition, all five infectious cases had died and the control hadn’t.

For a few minutes Jack thought that his painstaking efforts had been for naught, but then he got another idea. Since he’d typed the lists into the computer in the same order they’d been originally, he asked the computer to make the comparison prior to the first product used in the ICU.

As soon as Jack pushed his execute button the computer flashed its answer. The word “humidifier” appeared on the screen. Jack stared. Apparently the infectious cases had all used humidifiers from central supply; the control hadn’t. But was it a significant difference? From Jack’s childhood, he remembered his mother had put a humidifier in his room when he’d had the croup. He remembered the device as a small, boiling cauldron that sputtered and steamed at his bedside. So Jack could not imagine a humidifier having anything to do with spreading bacteria. At 212° Fahrenheit, it would boil bacteria.

But then Jack remembered the newer type of humidifier: the ultrasonic, cold humidifier. That, he realized, could be a totally different story.

Jack snatched up his phone and called the General. He asked to be put through to central supply. Mrs. Zarelli was off, so he asked to speak to the evening supervisor. Her name was Darlene Springborn. Jack explained who he was and then asked if central supply at the General handled the humidifiers.

“Certainly do,” Darlene said. “Especially during the winter months.”

“What kind does the hospital use?” Jack asked. “The steam type or the cold type?”

“The cold type almost exclusively,” Darlene said.

“When a humidifier comes back from a patient room what happens to it?” Jack asked.

“We take care of it,” Darlene said.

“Do you clean it?” Jack asked.

“Certainly,” Darlene said. “Plus we run them for a while to be sure they still function normally. Then we empty them and scrub them out. Why?”

“Are they always cleaned in the same location?” Jack asked.

“They are,” Darlene said. “We keep them in a small storeroom that has its own sink. Has there been a problem with the humidifiers?”

“I’m not sure,” Jack said. “But if so, I’ll let you or Mrs. Zarelli know.”

“I’d appreciate it,” Darlene said.

Jack disconnected but kept the phone in the crook of his shoulder while he got out Gloria Hernandez’s phone number. He punched in the digits and waited. A man answered who could speak only Spanish. After Jack struggled with a few broken phrases, the man told Jack to wait.

A younger voice came on the line. Jack assumed it was Juan. He asked the boy if he could speak to his mother.

“She’s very sick,” Juan said. “She’s coughing a lot and having trouble breathing.”

“Did she call the hospital like I urged?” Jack asked.

“No, she didn’t,” Juan said. “She said she didn’t want to bother anybody.”

“I’m going to call an ambulance to come and get her,” Jack said without hesitation. “You tell her to hold on, okay?”

“Okay,” Juan said.

“Meanwhile, could you ask her one question,” Jack said. “Could you ask her if she cleaned any humidifiers last night? You know what humidifiers are, don’t you?”

“Yeah, I know,” Juan said. “Just a minute.”

Jack waited nervously, tapping his fingers on top of Kevin Carpenter’s chart. To add to his guilt, he thought he should have followed up on his suggestion for Gloria to call Zimmerman. Juan came back on the line.

“She says thank you about the ambulance,” Juan said. “She was afraid to call herself because AmeriCare doesn’t pay unless a doctor says okay.”

“What about the humidifiers?” Jack asked.

“Yeah, she said she cleaned two or three. She couldn’t remember exactly.”

After Jack hung up from talking to the Hernandez boy he called 911 and dispatched an ambulance to the Hernandez residence. He told the dispatcher to inform the EMTs that it was an infectious case and that they should at least wear masks. He also told her that the patient should go to the Manhattan General and no place else.

With growing excitement, Jack placed a call to Kathy McBane. As late as it was, he didn’t expect to get her, but he was pleasantly surprised. She was still in her office. When Jack commented on the fact that she was still there after six, she said she’d probably be there for some time.