its mass, let’s say a fraction of an inch on the surface, may have become radioactive. Which would be a blessing,” Tiffin added. “That is, if you can find it at all.”

“We’ll find what’s left of it,” Jones said.

“Left of it? What are you talking about, Chief?” Herron asked.

“Irradiated gold,” Tiffin said, and he sounded indulgent, “has a half-life of one day. That means that after a day has passed, its radioactivity has reduced itself by half; the following day there is again a reduction to half of what was left, and so on. What remains, young man, is not gold. What remains is pure stable mercury.”

“You mean nothing may be left to that stuff except quicksilver?”

“Hardly, Mr. Herron. That kind of total deterioration of a large ingot would require more energy than our pile can muster. And besides, the thief wouldn’t have left here alive.”

“That’s good to know,” said Herron. “So we’re still looking for gold.”

“Considering our source of radiation and the possible length of time the ingot may have been exposed, the affected part of the gold would be quite small, but nonetheless dangerous. Of course, once the radiation has dissipated itself, the body of the ingot is again quite harmless. Pure gold, with traces of mercury.”

They left the storage room and went back to Tiffin’s office.

“Will there be anything else?” Tiffin stopped by the door.

“Just your report, Dr. Tiffin. We must know how sick the thief may be, and how dangerous the ingot may be to the population.”

“Mr. Jones, our guess as to how long the gold was exposed may not help you as much as you think. Nonlethal doses of radiation may cause a variety of symptoms, and they may appear to be harmless things.”

“What are they?” Jones asked.

“In general, the first signs are weariness, headache, digestive upset. The mucosa of the digestive tract seems particularly sensitive to radiation. Sometimes skin irritations occur, like a sunburn. In severe cases skin ulcerations develop or simple sores that refuse to heal. The most specific effect, of course, is the destruction of bone marrow with consequent blood deterioration. After that, any infection becomes a serious matter. But I’m sure you knew all this.”

“That much we knew, Dr. Tiffin. In the meantime, please hurry with your report.”

“I don’t see how a mere guess—”

“An intelligent guess, Dr. Tiffin. Good day, sir.”

Herron thought Jones had done that very well. He followed his chief down the long corridor and out into the open. The sun was shining and some new flowerbeds made a good smell in the air. Herron was glad to be out of the building. There hadn’t been any windows in the place.

They walked across the campus to the parking lot while Herron kept thinking about the things Tiffin had said.

“Has anybody answered our alarm yet, Chief?”

“Hundreds of hypochondriacs.”

“At least we’ll have our man worried.”

“Not necessarily, Herron. If he’s got half a brain, he’ll keep from exposing himself after hearing our alarm, and any mild symptoms he might get he’d be apt to overlook at first.”

“Till it gets worse.”

“It might, Herron. A few repeated exposures, each one of them small, and the effect will grow. At any rate, what have you found out in the meantime?”

Herron pulled a notebook out of his breast pocket and began to recite.

“Besides the Hamilton City case of radiation, no further reports, and they’re not sure it is radiation burn. Three of our sources report heavy spending by two of the suspects, Ham Lippin and Jerald Jenner. Ham is in Miami Beach and Jerry is in San Diego. I also got that list of parolees you asked for. It narrows down to seven: the two Corvetti brothers, Sam Nutchin, Gus Eisenberg, Tony Catell, Carl Lamotte, and Mug McFarlane. Three of them aren’t very likely, considering everything. Sam Nutchin is very sick, Tony Catell is a has-been without connections, and one of the Corvettis is drunk most of the time. So that leaves us with the younger Corvetti, Eisenberg, Lamotte, and McFarlane.”

“That leaves us with a lot of nothing.”

“Sorry, Chief, that’s as far as I could get, so far.”

They walked in silence till they came to the parking lot behind the library.

“Have the two watchmen come up with anything else?” Jones asked.

“Same story. Somebody slugged them from behind. They don’t know whether there was one or more assailants.”

“How are they getting along?”

“No change. Bad concussions.”

“Any new evidence that the lab boys dug up?”

“They find evidence of one person only.”

Jones and Herron got into the car. Jones took