“Terrorists.”

“Exactly.”

“Are you saying that this guy could just waltz into a hospital and get this stuff? Aren’t there regulations?”

Walling nodded.

“There are always regulations, Harry. But just having them is not always enough. Repetition, routine-these are the cracks in any security system. We used to leave the cockpit doors on commercial airlines unlocked. Now we don’t. It takes an event of life-altering consequences to change procedures and strengthen precautions. Do you understand what I am saying?”

He thought of the notations on the back of some of the ID cards in the victim’s Porsche. Could Stanley Kent have been so lax about the security of these materials that he wrote access combinations on the back of his ID cards? Bosch’s instincts told him the answer was probably yes.

“I understand,” he told Walling.

“So, then, if you were going to circumvent an existing security system, no matter how strong or weak, who would you go to?” she asked.

Bosch nodded.

“Somebody with intimate knowledge of that security system.”

“Exactly.”

Bosch turned onto Arrowhead Drive and started looking at address numbers on the curb.

“So you’re saying this could be an event of life-altering consequences?”

“No, I’m not saying that. Not yet.”

“Did you know Kent?”

Bosch looked at Walling as he asked and she looked surprised by the question. It had been a long shot but he threw it out there for the reaction, not necessarily the answer. Walling turned from him and looked out her window before answering. Bosch knew the move. A classic tell. He knew she would now lie to him.

“No, I never met the man.”

Bosch pulled into the next driveway and stopped the car.

“What are you doing?” she asked.

“This is it. It’s Kent ’s house.”

They were in front of a house that had no lights on inside or out. It looked like no one lived there.

“No, it isn’t,” Walling said. “His house is down another block and-”

She stopped when she realized Bosch had smoked her out. Bosch stared at her for a moment in the dark car before speaking.

“You want to level with me now or do you want to get out of the car?”

“Look, Harry, I told you. There are things I can’t-”

“Get out of the car, Agent Walling. I’ll handle this myself.”

“Look, you have to under-”

“This is a homicide. My homicide. Get out of the car.”

She didn’t move.

“I can make one phone call and you’d be removed from this investigation before you got back to the scene,” she said.

“Then do it. I’d rather be kicked to the curb right now than be a mushroom for the feds. Isn’t that one of the bureau’s slogans? Keep the locals in the dark and bury them in cow shit? Well, not me, not tonight and not on my own case.”

He started to reach across her lap to open her door. Walling pushed him back and raised her hands in surrender.

“All right, all right,” she said. “What is it you want to know?”

“I want the truth this time. All of it.”

BOSCH TURNED IN HIS SEAT TO LOOK directly at Walling. He was not going to move the car until she started talking.

“You obviously knew who Stanley Kent was and where he lived,” he said. “You lied to me. Now, was he a terrorist or not?”

“I told you, no, and that is the truth. He was a citizen. He was a physicist. He was on a watch list because he handled radioactive sources which could be used-in the wrong hands-to harm members of the public.”

“What are you talking about? How would this happen?”

“Through exposure. And that could take many different forms. Individual assault-you remember last Thanksgiving the Russian who was dosed with polonium in London? That was a specific target attack, though there were ancillary victims as well. The material Kent had access to could also be used on a larger scale-a mall, a subway, whatever. It all depends on the quantity and, of course, the delivery device.”

“Delivery device? Are you talking about a bomb? Somebody could make a dirty bomb with the stuff he handled?”

“In some applications, yes.”

“I thought that was an urban legend, that there’s never actually been a dirty bomb.”

“The official designation is IED-improvised explosive device. And put it this way, it’s only an urban legend until precisely the moment that the first one is detonated.”

Bosch nodded and got back on track. He gestured to the house in front of them.

“How did you know this isn’t the Kent house?”

Walling rubbed her forehead as though she were tired of his annoying questions and had a headache.

“Because I have been to his house before. Okay? Early last year my partner and I came to Kent ’s house and briefed him and his wife on the potential dangers of his profession. We did a security check on their home and told them to take precautions. We had been asked to do it by the Department of Homeland Security. Okay?”

“Yeah, okay. And was that routine for the Tactical Intelligence Unit and the Department of Homeland Security, or was that because there had been a threat to him?”

“Not a threat specifically aimed at him, no. Look, we’re wasting-”

“Then to who? A threat to who?”

Walling adjusted her position in the seat and let her breath out in exasperation.

“There wasn’t a threat to anyone specifically. We were simply taking precautions. Sixteen months ago someone entered a cancer clinic in Greensboro, North Carolina, circumvented elaborate security measures and removed twenty-two small tubes of a radioisotope called cesium one-thirty-seven. The legitimate medical use of this material in that setting was in the treatment of gynecological cancer. We don’t know who got in there or why, but the material was taken. When news of the theft went out on the wire somebody in the Joint Terrorism Task Force here in L.A. thought it would be a good idea to assess the security of these materials in local hospitals and to warn those who have access to and handle the stuff to take precautions and to be alert. Can we please go now?”

“And that was you.”

“Yes. You got it. It was the federal trickle-down theory at work. It fell to me and my partner to go out and talk to people like Stanley Kent. We met him and his wife at their house so we could do a security check of the place at the same time we told him that he should start watching his back. That is the same reason I was the one who got the call when his name came up on the flag.”

Bosch dropped the transmission into reverse and pulled quickly out of the driveway.

“Why didn’t you just tell me this up front?”

In the street the car jerked forward as Bosch threw it into drive.

“Because nobody got killed in Greensboro,” Walling said defiantly. “This whole thing could be something different. I was told to approach with caution and discretion. I’m sorry I lied to you.”

“A little late for that, Rachel. Did your people get the cesium back in Greensboro?”

She didn’t answer.

“Did you?”

“No, not yet. The word is that it was sold on the black market. The material itself is quite valuable on a monetary basis, even if used in the proper medical context. That’s why we are not sure what we’ve got here. That’s why I was sent.”

In ten more seconds they were at the correct block of Arrowhead Drive and Bosch started looking at address numbers again. But Walling directed him.

“That one up on the left, I think. With the black shutters. It’s hard to tell in the dark.”

Bosch pulled in and chunked the transmission into park before the car had stopped. He jumped out and headed to the front door. The house was dark. Not even the light over the door was lit. But as Bosch approached the front door he saw that it had been left ajar.

“It’s open,” he said.