The cop with the shepherd came out in front of a boulder pile and said, “You'd better take a look at this.”

Nature had arranged the rocks in a tight U, like a backless cave. The boulders were high- seven or eight feet tall- and there were cracks where the rocks pressed up against each other, invisible from below, but Petra could look between them and see the parking lot clearly.

Perfect vantage point for an observer.

And there'd been someone there observing. Recently.

The floor of the U was a soft bed of leaves. Petra was no forest ranger, but even she could see the body-shaped compression. Nearby was a piece of wrinkled yellow paper, darkening to brown translucence where grease had saturated it.

Food wrapper. Specks of something that looked like ground beef.

The shepherd had sniffed out bits of shredded lettuce, barely wilted, amid some dry leaves a few inches from the paper.

Petra sniffed the wrapper. Chili sauce. Last night's taco dinner?

Then the dog began nosing frantically at one corner of the U, and Stu summoned a tech over to check it out.

“Probably body fluid,” said the shepherd's handler. “He acts that way when he smells body fluid.”

Alan Lau came over. Petra noticed he had nervous hands.

A few minutes later, the field kit results: “Urine. On these leaves.”

“Human?”

“Human or ape,” said Lau.

“Well,” said Stu, “unless some chimp got loose from the zoo and bought himself dinner, it's probably safe to say Homo sapiens.”

Lau frowned. “Probably. Anything else?”

“Any other fluids?”

“Like blood?”

“Like anything, Alan.”

Lau flinched. “Not so far.”

“Check it out. Please.”

Lau returned to swabbing, dusting, probing. Susan Rose was summoned back to take pictures of the rocks. Petra sketched them anyway, then drifted away.

All that scientific work going on, but it was she who had the next find.

Twenty feet above the rocks, where she'd gone to explore because there was nothing for her to do and the dogs had moved on.

But they'd missed something, half concealed by leaves and pine needles. Flash of color beneath the green and brown.

Red. At first she thought: More blood, uh-oh. Then she bent and saw what it was; looked around for Stu.

He was back at the car, talking on his cell phone- the minuscule one his father the retired eye surgeon had given him for Christmas. Petra beckoned Lau. He sifted and found nothing around the red object, and Susan snapped away. They left, and Petra gloved up and picked it up.

A book. Thick, heavy hardcover; rebound in red leatherette. Library call number on the spine.

Our Presidents: The March of American History.

She flipped it open. L.A. Public Library, Hillhurst branch, the Los Feliz district.

Checkout card still in the pocket. Not much action on this one. Seven stamps in four years, the most recent nine months ago.

Stolen? Deacquisitioned? She knew the library got rid of stock all the time, because back in her starving artist days she'd filled her bookshelves with some great rejects.

She flipped pages. No deacquisition stamp, but that didn't prove anything.

Petra's mental camera began snapping. Had some homeless guy with an interest in U.S. history found himself a nice little natural lean-to where he could read and eat a taco and take a leak in the great wide open, only to witness a murder?

But no grease on the book, so maybe it had no connection to the person who sacked out behind the U-shaped rocks.

Or maybe Mr. Taco was a neat eater.

Even if the book was his, no big deal. There was nothing to say he'd been around precisely when Lisa Ramsey was being butchered.

Except for the fact that the urine was fresh. Within twelve hours, according to Lau, and Dr. Leavitt had estimated the murder at between midnight and 4 A.M.

A witness, or the murderer himself? The Fiend from the Hills hiding behind the rocks, waiting for the perfect victim.

Susan Rose had made the logical assumption that wife-beater Ramsey was the prime suspect, but other theories had to be considered.

But what would have brought Lisa Boehlinger-Ramsey to Griffith Park at night? And where was her car? Jacked? Was robbery the motive, after all?

Would someone this vicious need a motive?

A nut crime? Then why had the money been taken? Why not the jewelry?

Something didn't mesh. She just couldn't see a woman like Lisa coming alone to the park at that hour, all made up, wearing jewelry, that little black dress.

It spelled date. Out for the evening and she'd detoured. Or had been detoured. Why? By whom? Something hush-hush?

Buying drugs? There were lots of easier ways to score dope in L.A.

A date with the murderer? Had he driven her here with intent?

If Lisa had gone out on the town with a man, maybe someone had seen the two of them together.

One thing was sure: If it was a date, the lucky guy hadn't been some loner who read old library books and ate tacos and peed behind rocks.

Crashing in the park, no indoor plumbing, spelled homeless.

Modern-day caveman staking out his spot behind the rocks and marking it?

A spot from which he had a vantage view of the murder scene.

Or maybe he'd wet himself out of fear.

Seeing it.

Looking between those rocks and seeing it.

Almost there for sure now. The sun is out and I feel uncovered- like a target on a video game, something small that gets eaten.

I can walk forever if I have to. All I've done in L.A. is walk.

The bus let me off in a station full of people and echoes. Outside, the sky was a strange brownish gray and the air smelled bitter. I had no idea which way to go. In one direction were what looked like factories, power poles, trucks going back and forth. People seemed to be going the other way, so I followed them.

So much noise, everyone staring straight ahead. Between each block were alleys full of garbage cans with weird-looking guys sitting against the wall. Some of them watched me pass with cold eyes. I walked three blocks before I realized I was being followed by one of them, a real crazy-looking guy with rags around his head.

He saw me spot him and came at me faster. I ran and slid into the crowd, feeling the money in my shorts bouncing around but making sure not to touch it or look at it. Everyone was taller than me and I couldn't see too far in front of me. I kept pushing through, saying, “Excuse me,” and finally, two blocks later, he gave up and turned around.

My heart was going really fast and my mouth was dry. People kept piling onto the sidewalk, mostly Mexicans and a few Chinese. Some of the signs on restaurants were in Spanish and one huge movie theater with gold scrolls over the sign was playing something called Mi Vida, Mi Amor. A bunch of guys were selling fruit ices and churros and hot dogs from carts and now my mouth filled with spit. I started to wonder if I was dreaming or in some foreign country.

I walked till I found a street where the buildings were cleaner and newer. The nicest-looking building was something called the College Club, with U.S. and California flags out in front and a pink-faced guy in a gray uniform and hat with his arms folded across his chest. As I walked by he looked down his nose, as if I'd farted or done something rude. Then a long black car pulled up to the curb and all of a sudden he was just a servant, hurrying to open the door and saying, “How are you today, sir?” to a white-haired guy in a blue suit.

I made it to a little park that looked nice, with a fountain and some colorful statues, but when I got closer I saw that the benches were full of more weird guys. Right next door was a place called the Children's Museum, but no kids were going in. I was tired and hungry and thirsty, didn't want to spend any more of the Tampax money till I had a plan.