“LAMONT, THIS IS the last place in the universe we should be right now,” said Maddy, her voice muffled slightly by the panda mask. After the unproductive visit to Poole’s office that morning, Lamont had come up with another angle.

“Do you want to find your grandmother?” asked Lamont from behind the raccoon mask.

“Obviously I do,” said Maddy.

“Then we need to know what’s going on here,” said Lamont. “We need to find out where they’re holding people. For all we know, your grandmother could be here.”

They were standing across the street from the World President’s Residence, though Lamont insisted on calling it “my place.” From their position, they could see the whole rear of the house and the small balcony overlooking the back garden, although the garden itself was hidden behind a cement wall.

It was a warm night, and the neighborhood was crowded. There were the usual curious onlookers, a constant stream of official vehicles, and the usual heavy presence of TinGrin patrols and residential guards. Lamont had built his mansion to be secure. Now it was a fortress. And the rear gate was closed.

But not for long.

“There!” said Lamont. He pointed to an arriving van with an official emblem on the side. “Let’s go!” he said.

They moved quickly to a spot just across from the gate where the truck was idling. The driver was having a routine exchange with a gate guard. ID scan. Manifest check. All the while, the gate stayed open. Lamont and Maddy ducked back into an angle formed by intersecting hedgerows. A blind spot for security cameras, Lamont had calculated.

“Remember what we talked about,” he said, pulling off his mask.

“Stay focused. Stay calm. Don’t stretch it,” recited Maddy. Her mask yanked at her hair as she slid it off.

“Fifteen minutes, tops,” said Lamont. “Anything beyond that is too risky. Ready?”

“Ready,” Maddy answered.

They disappeared.

As the gate slid open, two young boys wandered past the small shelter where Maddy and Lamont had been standing. A raccoon mask and a panda mask lay on the ground. The boys scooped them up and ran off down the street.

One thing Maddy had learned about invisibility was the need to adjust her body movements to stay as quiet as possible. She was used to clomping around in heavy boots, but now she wore a pair of supple running shoes. She had learned to watch where she walked, to avoid puddles and dust that would show her footsteps. It wasn’t enough for her body and clothes to disappear; she had to remove all signs that she even existed. Part art. Part science.

And then there was the problem of staying out of Lamont’s way. When they were both invisible, she could see him but he could not see her. After having her toes stepped on a few times, she learned to synchronize her movements with his, even in close quarters.

But of course, to the guards, the van driver, and everybody else bustling around the mansion, they were both as invisible as air. Lamont and Maddy followed the van through the gates.

“Follow me!” Lamont whispered. He led the way to a set of stone stairs leading down from the parking area—toward the secret entrance he had used hundreds of times.

Back at the warehouse, Lamont had explained it all to Maddy, drawing elaborate diagrams on East River Storage stationery. He had designed the system himself and he was immensely proud of the whole setup: The button hidden beneath the crown of the entryway lamp. The secret door disguised as a stone wall. The complex assembly of gears, cables, and levers that made everything work seamlessly and silently.

“What makes you think any of that stuff is still there?” Maddy had asked. “It’s been over a century! We might as well be breaking into King Tut’s tomb!”

“Please,” said Lamont, insulted. “You don’t know anything about quality workmanship!”

The van was backed up near the rear wall of the mansion. Kitchen workers in white uniforms pulled crates and bins from the cargo area as the guards paced nearby.

Maddy was surprised that the antique carriage lamp was still there, mounted on the granite wall to the right of the door. Lamont reached for the top of the lamp, its copper plating now covered with green corrosion. His fingers clamped around the ornamental tip. He tried to turn it, but it was stuck shut. Maddy rolled her invisible eyes.

Lamont picked up a loose rock from the entryway. He held it about six inches from the lamp, ready to give it a solid tap. He looked over as the workers took the last of the supplies from the back of the van. The driver came around and put his palms against the doors. At the exact second he slammed the doors shut, Lamont whacked the stone against the crown of the lamp. The whole top of the lamp flew off, sending an ivory button flying, along with a few screws and a small bunch of brittle wires.

“Any other ideas?” whispered Maddy, her back pressed against the cold stone wall. Suddenly, she felt movement. She turned around. The secret door was opening! Unbelievable.

Shadow’s luck.