“What else can you remember about her?”

“Not much,” said Parks after a moment’s thought, “except…”

“Except what?”

“Except she was the only one who asked me about… McGuffin.”

“Professor Angus McGuffin?”

Parks registered surprise that they knew about him. “You’ve heard of him? Not many people have, outside the pseudoscience elite. He’s been dead these past sixteen years, a great loss to the conspiracy industry. When Guff was around, there was always lots of wild conjecture to try and dress up as serious scientific study.”

“What sort of work did McGuffin indulge in?” asked Jack.

“We don’t know for sure,” replied Parks, putting away his equipment and walking back to his van. “That’s what made him such catnip for the conspiracy industry. What we do know is that he liked blowing things up—big bangs, fireballs, that sort of stuff. He lost two fingers to a batch of nitroglycerine when he was still in the sixth grade. He was eventually expelled for blowing up the gymnasium with a form of homemade plastic explosive. By the time he was twenty-two, he had moved from rapid chemical decomposition to the power within the atom. He shared a Nobel Prize for Physics when he was only twenty-eight. He was brilliant, outspoken, daring. Best of all, he died while claiming he was ‘on the brink of a quantum change in atomic theory.’ Mind you, I suppose they all claim that.”

“Do you think his death at all mysterious?”

“Sadly, no,” replied Parks. “Fittingly, he blew himself up.”

“I heard. And his work at QuangTech?”

“The official story is that he was transforming grass cuttings into crude oil, but it’s doubtful someone as savvy as the Quangle-Wangle would fall for that old con trick. His work was top secret, but even now he still holds the record for blowing up laboratories. Thirty-one in under twenty years, if you count his school experiments.”

“What about farther afield?” suggested Jack. “Such as the Nullarbor in ’92, Tunbridge Wells in ’94 or Pasadena in ’99?”

Parks stopped and stared at them both. “Hooey. Not even the staunchest theorist would connect those with Guff.”

“He was too underqualified?”

“He was too dead. Those happened after his accident. No one seriously doubts that he died, Inspector. If you’re after truth, I’m not sure the conspiracy fraternity is the place to find it.”

Jack looked around at the fresh topsoil and said, “Do you want to see a part of Mr. Cripps’s garden before it was taken away?”

Parks’s eyes nearly popped out on springs.

Jack took the package from his pocket and passed it across. Dr. Parks led them to the back of his van, donned a pair of latex gloves and delicately removed the small piece of fired glassy earth from the mailing envelope.

“This is good,” he said quietly, “really good. Do you have any provenance for it?”

“Sadly, no.”

“Excellent. Reliable provenance has always seriously damaged the conspiracy industry. Do you see how smooth and glassy one side is while the other side is fired into a hard terra-cotta?”

“Yes?”

“This is the remains of one of Mr. Cripps’s gravel paths. The sand has fused into glass, the soil beneath it into a ceramic. The principle of firing pottery is the same, only instead of several hours at a relatively low temperature, this was done in a fraction of a second—but at several hundreds of thousands of degrees. No wonder they didn’t want us to see it.”

“Why?”

“Because it proves it wasn’t a conventional explosion. The damage you see around you could easily have been done by an unexploded wartime bomb, but with this evidence of associated heat”—he waved the piece of fired earth at them—“it’s quite impossible. Conventional explosives just don’t match the heat generated by… nukes.”

“Wait, wait, wait,” said Jack, who was willing to go a few steps into the conspiracy world, but not the several hundred yards Parks was suddenly demanding. “You’re saying someone was using a nuclear weapon in Berkshire? Surely cucumber fanciers aren’t that serious over the opposition?”

“Extremism comes in all shapes and forms, Inspector. But you’re right to be skeptical. Let’s see what we can find out about this object of yours.”

He opened a small wooden box and took out a device that began giving off random clicks when he switched it on.

“This Geiger counter measures radioactivity,” he explained.

“The more clicks, the higher the levels—the odd clicking you can hear is just background radiation.”

He passed the instrument over the sample, and there were a few extra clicks, but nothing wildly dramatic.

“You see?” asked Parks.

“No.”

“The nuclear-blast theory seems sound until one looks for evidence of radioactivity—and there’s hardly any at all.”

“I’m no expert in nuclear weapons, Dr. Parks,” admitted Jack.

“Perhaps you can explain that in simpler terms.”

Parks took a deep breath. “Atom-splitting reactions are called fission devices: the A-bomb. Atom-fusing reactions are called fusion devices. A nuke small enough to do the limited damage you see here would have to be a fission device.”

“Why?” asked Mary.

“Simply stated, an A-bomb is the bringing to critical mass of a quantity of fissile material, say uranium 235. A lump of uranium 235 the size of a football would be critical; a lump the size of a golf ball would not.”

“I get it,” said Jack. “Just add two uncritical masses together and bang, right?”

“In essence. However, you can ignite even smaller lumps of fissile material by bringing them together very rapidly. In theory you could make an A-bomb to fit in a suitcase. A mini-nuke with limited destructive power.”

“And that was what hit Cripps?”

“No. A-bombs give off large quantities of radioactive fallout. There is nothing at the site, nothing downwind and only a small amount on this sample. This could not have been a fission device.”

“What then?”

“A fusion reaction with the heavy isotope of hydrogen as the fuel would give a waste product of only helium and a small amount of localized radioactivity caused by an excess of neutrons. However, there are problems here, too.”

“Such as?”

“To start a fusion reaction, you need a huge amount of heat—two million degrees or more. To get that you need either a plasma chamber the size of a house consuming vast quantities of power, a ball of gas the size of the sun or—”

“An A-bomb?” suggested Mary.

“Precisely. A fission trigger to set off the fusion device—but that would also leave large quantities of detectable radioactive fallout.”

He waved the Geiger counter over the fused earth again, and it clicked in a desultory manner.

“This is just mildly radioactive, so it suggests that it might have been a fusion blast of a very small size. Since nuclear fusion exists only in the heart of stars, an A-bomb or a plasma chamber, I think this was something else entirely—a ground burst of a type we have yet to fully understand.”

There was a brief silence as Jack and Mary tried to figure out just what Parks was talking about. As far as Jack could make out, Cripps and his garden were destroyed by a destructive force that Parks couldn’t explain and that the government was keen on hiding—they had removed nearly eighty tons of topsoil before allowing anyone in.

“Do you know the significance of this shape?” asked Parks, indicating the rectangular block of fired earth. Jack and Mary said nothing, so he continued. “If this did come from here, it was cut when the glass was still hot. There was only a time window of twenty-six minutes before the area was cordoned off. The first officers on the scene saw no one but confused villagers. If that’s correct, then we have a witness to the event. Find him and you’ll answer a lot of questions.”