“How will you trap him?” Roger asked.
When his cousin outlined his plan, Roger was animated.
“It might work,” he exclaimed, “He will turn out to be the one who brought the white rats. They were trained, too, maybe.”
“I wondered that you did not see why I bought back issues of the newspapers,” Grover told him, “I had one idea that the thing might have been done by some zoo keeper; but the more possible notion was that some vaudeville act had trained animals. Now we do not need to comb through the advertisements of the theatre section. We know, by logical deduction, that we would find it.”
Roger, and Potts, carrying out instructions about which they said nothing to any member of the staff, assembled a mass of materials, apparatus and paraphernalia.
There were microphones; and they employed the laboratory’s device for producing infra-red rays, as well as a number of small cameras for taking motion pictures which Potts secured; to each one they applied a shutter-trip suggested by Grover, that would operate when a light-beam of the infra-red variety might be unknowingly broken by an intruder.
Other parts, and wiring by the yard, they connected up.
“But I don’t understand it,” Potts argued as they worked. “It’s all right to say a monkey climbed in through the skylight way; but how does that fit the snake-trail up the stairway?”
“I asked about that,” Roger told him, “Cousin Grover was more in a joking humor than I ever saw him, and he said I’d done so well, he would leave that for me to work out, too.”
“Did you?”