Tom thought hard. "None. If I had detected any special sounds during the call, I'm sure they would have stuck in my mind." Ames tried another tack. He asked how many people had known about the expected arrival of the brain energy from space. This was harder to answer, but as Tom and his father enumerated the persons, it did help to narrow the circle of suspects. Besides the Swifts, Chow, Phyl, Ames, and George Dilling, there were three groups who had had access to the information. One was the radio operators at the space-communications laboratory. Another consisted of Arv Hanson and Hank Sterling and the workmen who had taken part in building the energy container. The last group, which also included Hank and Arv, were the technicians who had actually gone to the hillside to await the visitor from Planet X. Tom scowled. "None of those people would pull such a trick, Harlan--any more than the ones like you and Arv and Hank who are above suspicion. Most of them could have easily obtained the news without going through such a rigmarole." Mr. Swift nodded. "Tom's right. Unless, of course, they had some urgent reason for wanting to find out as soon as possible." "Which makes me think it may have been an outsider after all," Tom argued. "Remember, the Brungarians may have intercepted the code messages to or from our space friends." After a moment's silence, he added gloomily, "Whoever the caller was, he knew the energy was arriving. And now he knows it's here!" Bud interjected, "Well, if he was a Brungarian agent and he's hoping to steal the brain energy, one thing's sure. No earthquake will demolish this place as long as the energy is here at Enterprises." "A comforting thought, Bud," Mr. Swift commented with a wry smile. Again Tom frowned. "At any rate, Harlan, see if you can get a line on that impostor." Ames departed to begin a thorough check of all personnel at the plant who might have been implicated. Bud went on an errand, as Tom began showing his father the accomplishments of the space robot. "We've christened him Exman," Tom said. By means of the electronic brain, he made the visitor do a number of maneuvers in response to orders. "Wonderful!" Mr. Swift exclaimed, greatly impressed. "Let's see if he can use his caterpillar treads as well as he does the wheels." Tom brought a small flight of portable aluminum stairs which he used for reaching up on high shelves or tinkering with outsized machines. Tom was uncertain at first how to code the command, having no symbol for steps or stairs. Finally he moved Exman to the bottom of the steps and signaled simply: _Go up!_ Exman paused for a moment, then attempted the ascent. His caterpillar tracks clawed their way up the first step. Then, gingerly, he essayed the next. The robot body tilted, but its gyro kept it from toppling over.