"Hand it over," the man said.
Dennison was stunned. How could anyone have known about his discovery? And how could they dare try to rob him in a public subway car?
Then he realized that they were probably just after his money.
"I don't have much on me," Dennison said hoarsely, reaching for his wallet.
The man on his left leaned over and slapped the briefcase. "Not money," he said. "The immortality stuff."
In some unaccountable fashion, they knew. What if he refused to give up his briefcase? Would they dare fire the automatic in the subway? It was a very small caliber weapon. Its noise might not even be heard above the subway's roar. And probably they felt justified in taking the risk for a prize as great as the one Dennison carried.
He looked at them quickly. They were mild-looking men, quietly, almost somberly dressed. Something about their clothing jogged Dennison's memory unpleasantly, but he didn't have time to place the recollection. The automatic was digging painfully into his ribs.
The subway was coming to a station. Dennison glanced at the man on his left and caught the glint of light on a tiny hypodermic.
Many inventors, involved only in their own thoughts, are slow of reaction. But Dennison had been a gunnery officer in the Navy and had seen his share of action. He was damned if he was going to give up his invention so easily.