Robert stiffened.
Caleb continued.
"And it isn't."
The hangar became silent.
Vivien narrowed her eyes.
"Then what is it?"
Caleb looked at the aircraft.
"Something has been made to look broken."
Patrick folded his arms.
"Excuse me?"
Caleb ignored him.
"It passes your diagnostics because whoever did it understood your diagnostics."
Robert's expression changed.
Caleb pointed toward the nose gear.
"There's a vibration here."
He pointed toward the wing.
"There's another anomaly there."
Then he pointed toward the rear of the aircraft.
"And something doesn't belong back there."
Vivien stared at the three chalk circles.
"You think the aircraft was sabotaged?"
Caleb met her eyes.
"I think you have seven minutes before you need to leave for the airfield gate."
He paused.
"I can show you what I'm seeing in less than seven minutes."
Vivien looked at her watch.
6:43.
She had seven minutes.
"Do it."
Caleb nodded.
And for the first time that morning, everyone in Hangar 4 stopped looking at the aircraft.
They started looking at him.
Seven Minutes
Caleb returned to the first circle.
"Put your hand here."
Robert Tran hesitated.
Then he crouched.
He placed his palm against the concrete.
"Feel anything?"
Robert shook his head.
"Wait."
They waited.
Three seconds.
Five.
Seven.
Then Robert's eyebrows moved.
"There's something."
"What?"
"A vibration."
Caleb nodded.
"That's what I felt."
Patrick stepped forward.
"The engine isn't running."
"I know."
"So where is the vibration coming from?"
"That's what we're going to find out."
Caleb looked toward the electrical panel.
"Is the aircraft drawing power?"
"Yes."
"Even though the start sequence has failed?"
Robert checked his tablet.
"Minimal auxiliary load."
"Minimal isn't zero."
Robert looked again.
Caleb said, "Something is cycling."
Robert frowned.
"That's impossible."
"Then prove me wrong."
The words were not arrogant.
That was what made them uncomfortable.
Caleb wasn't challenging Robert's intelligence.
He was challenging the assumption that the aircraft was behaving normally.
Robert signaled to another engineer.
"Check auxiliary systems."
The engineer moved toward the panel.
Caleb went to the second circle.
"This is where I want the fuel line pressure checked."
Patrick laughed again.
"You're diagnosing a fuel system from concrete?"
Caleb looked at him.
"No."
He pointed to the floor.
"I'm using the floor to tell me where to look."
Patrick opened his mouth.
Caleb continued before he could answer.
"There's a difference."
Robert looked at Caleb.
"What exactly are you seeing?"
"Something repeated."
"What?"
"The vibration."
Caleb tapped the concrete.
"Normal mechanical failures produce patterns, but those patterns change when the system changes."
He pointed toward the Gulfstream.
"This doesn't."
He looked at Robert.
"Something is deliberately maintaining a false condition."
Robert's face tightened.
"That's a serious claim."
"I know."
"Do you have evidence?"
"Not yet."
Caleb pointed toward the access panel.
"Open that."
Robert hesitated.
Then he nodded.
The panel was removed.
A junior engineer climbed into the cockpit.
"Digital fuel pressure?"
"Nominal."
Caleb said, "Analog."
The junior engineer paused.
"Analog backup?"
"Yes."
He checked.
Silence.
Then—
"That's different."
Robert turned.
"How different?"
The engineer read the number.
Robert's face went pale.
Patrick stepped closer.
"That can't be right."
"It is."
Caleb looked at Vivien.
"The digital system is receiving false information."
Vivien's voice was quiet.
"Meaning?"
"The fuel pressure isn't what your computer thinks it is."
Robert stared at the readings.
Caleb continued.
"A mechanical failure would be one possibility."
Robert nodded slowly.
"But?"
"But the difference is consistent."
Caleb tapped the digital display.
"If the sensor were damaged randomly, the numbers would fluctuate."
He pointed toward the analog gauge.
"They don't."
He looked at Vivien.
"Someone wants your diagnostics to report normal pressure."
Nobody spoke.
The meaning settled over the hangar.
Vivien's face hardened.
"Sabotage."
Caleb didn't answer.
He moved toward the third circle.
"This is where I need your best fuel-systems engineer."
Robert followed.
"Why?"
"Because I don't know this airframe well enough to tell you what belongs here."
He pointed beneath the rear fuselage.
"But I know what shouldn't."
Robert opened the service panel.
For several seconds, there was only the sound of metal latches.
Then Robert stopped.
His flashlight froze.
"What?"
Vivien stepped closer.
Robert didn't answer.
He reached farther into the compartment.
"There is a valve here."
Caleb looked at him.
"What kind?"
"I don't know."
"Should it be there?"
Robert swallowed.
"No."
He pulled the component into view.
It was small.
Almost insignificant.
A carefully installed valve had been integrated into the fuel return line.
Its wiring had been tied into an existing harness.
To an untrained eye, it looked like factory equipment.
Robert traced the wiring.
"This isn't on the schematic."
Caleb asked, "What does it do?"
Robert studied it.
"I think it restricts fuel flow."
"Under what condition?"
Robert followed another wire.
His expression changed.
"Altitude."
Vivien stared at him.
"What happens if the aircraft climbs?"
Robert didn't answer immediately.
Caleb did.
"The valve restricts the fuel return."
Robert nodded.
"At altitude, the system could lose fuel stability."
"How long?"
Robert looked at the aircraft.