Claire is chief medical examiner of San Francisco. She's a forensic pathologist, not a cop.

"You think it was personal? That he targeted your mom? Knew her?"

Willie shook his head. "I was helping to tie up the boat when the screaming started," he told me. "He shot some other people first. My mom was the last one. He had a gun right up to her head. I grabbed an iron pipe," he said. "I was going to brain him with it, but he shot at me. Then he jumped overboard. I went after him – but I lost him."

It really hit me then.

What Willie had done. My voice was loud, and I grabbed his shoulders.

"What if you'd caught up with him? Willie, did you think about that? That 'skinny white man' was armed. He would have killed you."

Tears jumped out of Willie's eyes, rolled down his sweet, young face. I relaxed my grip on his shoulders, took him into my arms.

"But you were very brave, Willie," I said. "You were very brave to stand up to a killer to protect your mom.

"I think you saved her life."

I KISSED WILLIE'S CHEEK through the open patrol-car window. Then Officer Pat Noonan drove Willie to the hospital and I boarded the ferry, joining Tracchio in the open front compartment of the Del Norte's top deck.

It was a scene of unforgettable horror. Bodies lying where they'd fallen on the thirty or forty square yards of bloody fiberglass deck, footprints leaving tracks in all directions. Articles of clothing had been dropped here and there – a red baseball cap was squashed underfoot, mixed with paper cups and hot dog wrappers and newspapers soaked in blood.

I felt a sickening wave of despair. The killer could be anywhere, and evidence that might lead us to him had been lost every time a cop or a passenger or a paramedic walked across the deck.

Plus, I couldn't stop thinking about Claire.

"You okay?" Tracchio asked me.

I nodded, afraid that if I started to cry, I wouldn't be able to stop.

"This is Andrea Canello," Tracchio said, pointing to the body of a woman in tan pants and a white blouse lying up against the hull. "According to that fellow over there," he said, pointing to a teenager with spiky hair and a sunburned nose, "the doer shot her first. Then he shot her son. A little kid. About nine."

"The boy going to make it?" I asked.

Tracchio shrugged. "He lost a lot of blood." He pointed to another body, a male Caucasian, white haired, looked to be in his fifties, lying halfway under a bench.

"Per Conrad. Engineer. Worked on the ferry. Probably heard the shots and tried to help. And this fellow," he said, indicating an Asian man lying flat on his back in the center of the deck, "is Lester Ng. Insurance salesman. Another guy who could have been a hero. Witnesses say it all went down in two or three minutes."

I started picturing the scene in my head, using what Willie had told me, what Tracchio was telling me now, looking at the evidence, trying to fit the pieces into something that made sense.

I wondered if the shooting spree had been planned or if something had set the shooter off and, if so, what that trigger had been.

"One of the passengers thinks he saw the shooter sitting alone before the incident. Over there," Tracchio told me. "Thinks he was smoking a cigarette. A package of Turkish Specials was found under a table."

I followed Tracchio to the stern, where several horrified passengers sat on an upholstered bench that wrapped around the inner curve of the railing. Some of them were blood spattered. Some held hands. Shock had frozen their faces.

Uniforms were still taking down the witnesses' names and phone numbers, getting statements. Sergeant Lexi Rose turned toward us, saying, "Chief, Lieutenant. Mr. Jack Rooney here has some good news for us."

An elderly man in a bright-red nylon jacket stepped forward. He wore big-frame eyeglasses and a digital Minicam about the size of a bar of soap hanging from a black cord around his neck. He had an expression of grim satisfaction.

"I've got him right here," Rooney said, holding up his camera. "I got that psycho right in the act."

THE HEAD OF THE Crime Scene Unit, Charlie Clapper, crossed the gangway with his team and came on board moments after the witnesses were released. Charlie stopped in front of us, greeted the chief, said, "Hey, Lindsay," and took a look around.

Then he dug into the pockets of his herringbone tweed jacket, pulled out latex gloves, and snapped them on.

"This is a fine kettle of fish," he said.

"Let's try to stay positive," I said, unable to conceal the edge in my voice.

"Cockeyed optimist," he said. "That's me."

I stood with Tracchio as the CSU team fanned out, putting out markers, photographing the bodies and the blood that was spattered everywhere.

They dug out a projectile from the hull, and they bagged an item that might lead us to a killer: the half-empty packet of Turkish cigarettes that had been found under a table in the stern.

"I'm going to take off now, Lieutenant," Tracchio told me, looking down at his Rolex. "I have a meeting with the mayor."

"I want to work this case – personally," I said.

He gave me a hard, unblinking stare. I'd just pushed a hot button on his console, but it couldn't be helped.

Tracchio was a decent guy, and mostly I liked him. But the chief had come up through the ranks by way of administration. He'd never worked a case in his life, and that made him see things one way.

He wanted me to do my job from my desk.

And I did my best work on the street.

The last time I'd told Tracchio that I wanted to work cases "hands-on," he'd told me that I was ungrateful, that I had a lot to learn about leading a command, that I should do my goddamned job and feel lucky about my promotion to lieutenant.

He reminded me now, sharply, that one of my partners had been killed on the street and that only months ago, Jacobi and I had both been shot in a desolate alley in the Tenderloin. It was true. We'd both nearly died.

Today, I knew he couldn't turn me down. My best friend had a slug through her chest, and the shooter was free.

"I'll work with Jacobi and Conklin. A three-man team. I'll have McNeil and Chi back us up. Pull in the rest of the squad as needed."

Tracchio nodded reluctantly, but it was a green light. I thanked him and called Jacobi on my cell. Then I phoned the hospital, got a kindhearted nurse on the line who told me that Claire was still in surgery.

I left the scene with Jack Rooney's camera in hand, planning to look at the video back at the Hall, see the shooting for myself.

I walked down the gangway and muttered, "Nuts," before I reached the pavement. Reporters from three local TV stations and the Chronicle were waiting for me. I knew them all.

Cameras clicked and zoomed. Microphones were pushed up to my face.

"Was this a terrorist attack, Lieutenant?"

"Who did the shooting?"

"How many people were killed?"

"Give me a break, guys. The crime just happened this morning," I said, wishing these reporters had grabbed Tracchio or any one of the other four dozen cops milling around the perimeter who'd love to see themselves on the six o'clock news.

"We'll release the names of the victims after we've contacted their families.

"And we will find whoever did this terrible thing," I said with both hope and conviction. "He will not get away."