“Shaped charge.”

“Sometimes called hollow charge.”

Bell and Archie rejoined the others at the table.

Mack said, “This politician bought himself a big safe with six-inch walls made of plates of iron and steel.”

“In the event,” Wally explained to Archie, “that a city contractor or a police chief or a sporting house proprietor had a sudden need to safeguard some cash and it was after banking hours, this politician would help out by holding it for them in his safe.”

Archie nodded.

“Performing a public service.”

“Some safecracker,” Mack continued, “tried to blow it. Seeing six-inch walls, the yegg applied enough dynamite to blast the roof off the politician’s house. Which it did, but only dented the safe. Barely scratched it. A while later, along comes Rosania. He’s caught wind that the politician purchased diamonds for his girl. Rosania blows a hole in the six-inch walls big enough to stick his hand in. Like it was made of cardboard. And no one even heard the explosion.”

“How’d he do it?” asked Bell.

“Rosania’s one of those fellows who’s always got his nose in a book,” said Fulton.

Kisley said, “He read about this scientist at the Naval Torpedo Station up in Newport, Rhode Island, who came up with this big idea called a hollow charge. Sometimes they call it a shaped charge ’cause where you make it hollow, the direction its hollow points is the direction where the explosion goes. Instead of blowing off the politician’s new roof, Rosania drove all that dynamite in the exact direction he wanted, straight through the wall of the safe. Quiet little poof. Four-inch hole.”

“Did he get the diamonds?” asked Archie Abbott.

Mack Fulton looked at the apprentice incredulously. “What? No, he got diamond dust and diamond flakes.”

“I thought diamonds were indestructible.”

“So did Rosania,” said Mack Fulton.

Wally Kisley laughed. “Clearly, the safecracking classes have some experimenting still to do. But, Isaac, if your saboteur found a way to stick a hollow charge to the chain bridle, he wouldn’t need a big bunch of sticks of dynamite you’d spot a mile off. Fact is, I don’t think he used a cold chisel at all. I think that hollow charge did the job all by itself. What you heard, Isaac, was a small charge of dynamite blowing all in one direction straight at this link—so concentrated that it sheared the chain like a chisel.”

“But how long would the charge stick to the chain? Jerking around like it does.”

Kisley shrugged. “Not long. Maybe he wired it on. You said you never found that shackle. I bet he packed the entire charge inside the shackle.”

Mack Fulton said, “Maybe you couldn’t find the shackle because all that was left was shackle chips and shackle dust.”

Bell stared at Fulton. For a second he felt the floor shift under him. Like a dream remembered days later, he could almost see a pair of golden eyes, wolf eyes, from which exploded a fist. The white-damp dream in which he thought he had seen the shackle he never found. He shook his head, wondering how to unscramble tangled memory, and pressed on. “It doesn’t take much shaking to explode fulminate of mercury. How long before the winch jerking the wire set off the detonator?”