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?”