Instinctively they all drew their pistols.

Limon smacked Guerner in the arm. "Jesus, what are we, idiots? This is a trick." He still didn't lower his pistol.

Guerner focused on the staircase. "I know. But it's a fucking impressive one."

The footsteps were moving across the floor to them now.

Guerner motioned toward the front door. "Let's back it up, guys."

Then, in midair not five feet in front of them, a man's voice shouted, "You don't belong here!"

What happened next surprised even the veteran Guerner. The deepest sound he'd ever felt passed over and through him. Then it was quiet, until the mission table near him began to vibrate so violently it started moving across the floor. A crystal vase on top of it shattered.

Suddenly Guerner felt as though someone had grabbed his intestines straight through his Kevlar suit. He didn't even have time to warn Limon and Chapman before he was doubled over on the marble floor, vomiting. His guts felt like writhing snakes trying to climb out of his body. The agony was intense. His whole being was gripped with a deep and primordial feeling of dread-like a palpable evil had climbed inside him.

Guerner was a man of science and reasoning, but his entire knowledge of the world fled, leaving him alone on the floor weeping in terror. He crawled away through his vomit, listening to insane shrieking. Then he realized the shrieks were coming from him.

Sebeck, Ross, and Mantz stood with the gathered officers in the courtyard. A moment ago they had heard Guerner shout a warning to someone in the house. Chief Eichhorn leaned over to the caretaker to confirm that no one else was in the mansion.

Sebeck's cell phone twittered. He pulled it from his belt clip. "Sebeck."

A voice he vaguely recognized said, "Detective Sebeck, I just needed to know where you were."The connection dissolved in a flurry of static.

Mantz noticed Sebeck's stunned expression. "Who was it, Pete?"

Sebeck stared at his phone, then looked to Ross. "I'm not certain, but I think that was Matthew Sobol…"

That's when the shrieking began. They were the most bloodcurdling shrieks Sebeck had ever heard, like a man burning alive. Agents and officers pelted toward the front door. Before they got far, Decker shouted, "Don't go inside! Stay clear!"

They slowed for a second, but then they saw Limon clawing his way out the open front door on his hands and knees. His Kevlar vest was covered in vomit, and his helmet was off. He was bleeding from the nose, eyes, and ears and groped along as if blind.

Sebeck and some of the others rushed to his aid. Limon was still sixty feet away from them. Eichhorn and Decker shouted for caution, and with all eyes looking forward, no one noticed the middle garage door silently rise behind them.

The first warning they received was the guttural sound of a powerful engine, then screeching tires. Sebeck and the other officers turned to face a full-sized black Hummer roaring out of the garage. It bore down on the nearest of them and crushed a deputy and an FBI agent into the side of an FBI sedan, hitting it so hard the car slid into the police cruiser behind it.

Sebeck stood in a paralysis of incomprehension. He could clearly see that no one was driving the Hummer. It sported six tall whip antennas-still wagging from the impact of the collision-and it had odd-looking sensors bolted to its hood, roof, and fenders.

The Hummer's engine roared as it backed away from the wrecked car and the bodies tumbled onto the paving stones. The Hummer's push-bar bumper was barely dented and was covered in blood.

It all happened so fast. Two men had just been killed. Adrenaline flooded into Sebeck's system.

People ran in every direction, shouting. Sebeck looked back to the door of the mansion to see the other two bomb squad members running out of the house, screaming. One of them stumbled down the front steps and fell into the flower beds, where he went into convulsions.

Deputies and FBI agents drew pistols and fired at the Hummer as it screeched around the edge of the courtyard, building up speed again. Shots cracked in rapid succession, echoing against the side of the house. The familiar, pungent smell of smokeless powder brought Sebeck to his senses, and he pulled his Beretta from its holster. He rammed its slide back, gripped it with both hands, then opened fire. He aimed for the Hummer's tires.

Sebeck could clearly see bullet impacts on the tires, but they had no effect. The tires were either run-flat or solid rubber. He brought his aim up to the windows-but remembered there was no one to shoot at.

Now the Hummer howled straight back toward them. Deputies and agents fired a few frantic last shots before scrambling from between the parked police vehicles. It crashed into the side of another patrol car, halving the car's width and driving it back like a battering ram into two more cruisers. Those cars smashed into the patio wall, pinning a couple of officers there. The sheer force and loudness of the crash sent Sebeck running for the nearest high ground-a garden wall.

Screams of pain came to his ears from the pinned officers. He looked back and saw the Hummer seesawing backward as its gears whined. It swung wide and winged a fleeing officer with its fender. The man went rolling across the courtyard. Turning on him, the Hummer screeched forward before he could get up. The deputy went shrieking under its wheels. His body was dragged halfway across the courtyard before it fell loose.

Sebeck screamed in rage and emptied his pistol at the rear of the Hummer while it chased down two agents fleeing toward a garden pond.

An agent with a pump shotgun ran up to it as it passed by. He fired two rounds into it, blasting out its windows and sending pieces of plastic flying. He kept firing as it drove on.

Shouts filled the courtyard now. Nearby, Sebeck saw Decker screaming into his radio, "…do you copy?"

Back at the estate gates, Deputy Karla Gleason stood taking in the sun and watching for the expected arrival of the media. There hadn't been any radio calls from the mansion-which was odd-but she stood next to her patrol car, attentive and wondering what the mansion would fetch on the real estate market.

Across the driveway, Deputy Gil Trevetti stood next to his cruiser, waving a curious passenger car on by. That's when the crackling of gunfire reached Gleason's ears. She and Trevetti exchanged looks, then ran for the fence line.

Everything looked normal. The mansion was partially masked by trees, so none of the police vehicles were visible from here. But now the gunfire crackled like firecrackers. It was an unbelievable amount of sustained shooting. Maybe it wasfireworks.

Gleason pressed the button on her shoulder radio. "Unit 920 to any available Blue Team member: 10–73?"

No response.

"Repeat. Unit 920 to any available Blue Team member: 10–73?"

A distant truck engine raced, then a crash.

"What the hell's going on, Gil?"

The unmistakable boom of a shotgun reached them over the grounds. Five shots in five seconds. Gleason shot skeet. She knew that sound well. She pressed the button on her shoulder radio. "920 to Control, multiple 10–57 at 1215 Potrero Road. Repeat, multiple, multiple 10–57. Code 30. Radio contact lost with Blue Team."

The courtyard was chaos as the Hummer roared back in from the garden and smashed headlong into the ambulance, sending glass and metal debris flying. It surged ahead, pushing the ambulance sideways at the mouth of the driveway-blocking the exit.

The entire time, officers laid down sustained gunfire on it, pocking its body with bullet holes. The bullets didn't appear to have much effect, even though some of the Hummer's sensors now dangled loose on wires.