In the midst of the tale, a car was heard on the driveway, and a minute later Mr. Nichols entered the house. Although he was never inclined to be demonstrative, the detective clasped his daughter in his arms and Penny noticed that his hands trembled slightly.
"I've just heard the entire story at the police station," he told her. "You gave me a terrific scare, Penny."
"I gave myself one, too. If it hadn't been for your men who shadowed me, I'm afraid I'd never have returned to tell the tale."
"I doubt that the gangsters would have actually harmed you, but they would have used you as a weapon to strike back at me. I am sorry about having you trailed, Penny, but you understand my position. I was afraid of this very thing."
"It's all right," Penny smiled. "Only your men aren't so clever at keeping me in sight. I unintentionally gave them the slip earlier in the evening."
Mrs. Gallup had gone to the kitchen to prepare sandwiches and an iced drink. Taking advantage of her absence, Penny gave a detailed report of her visit to the Hamilton Plant. At first her father listened almost incredulously.
"It sounds fantastic, Penny. And yet, it's just the sort of trickery which would appeal to Rap Molberg. You say the door is operated by means of a photo-electric cell?"
"That's what I think. At least when the beam of my light struck a certain spot on the wall, the door opened."
Mr. Nichols arose and paced rapidly back and forth across the floor.
"I'm going to take you into my confidence, Penny," he said quietly. "For days my men have been circling in on Rap and his gang. We've located one of their hideouts, and we're raiding the place tomorrow night. It now seems advisable to surround the Hamilton building simultaneously. Then there will be no chance that any of the crooks can use the underground ramp to make a get-away."