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.

“Bravo!” Mr. Swift applauded encouragingly.  But the next instant Exman gave up!  He slid back to the floor again with a heavy bump.  Then he began whirling and darting about madly.

“Good night!  Exman’s gone berserk!” Tom cried.

Now wafts of smoke could be seen issuing from the robot’s wheels.  He was banging wildly about the laboratory, leaving a trail of havoc.

Bud, who had returned, opened the door to come in.  Instantly Exman lunged toward him, antennas sparking fiercely and wheels smoking.  Bud slammed the door hastily.

The Swifts, too, found it wiser to take cover.  They crouched behind a lab workbench until the frenzy was over.  Presently Exman subsided and rolled to a complete standstill.

“Good grief!” Tom stood up cautiously and eyed the creature.  It made no further move.  Bud poked his head through the doorway for a wary look, then re-entered the laboratory.

“What made him blow his top?” Bud asked.

Then Tom heard a quiet chuckle from his father.  “Actually, boys,” the elder scientist said, “I think we should be encouraged.”