She was on her knees trying to get to her feet when she saw the extraordinary pale face of baby Ethel so deeply, peacefully, in sleep despite the screaming. Then the woman who called out stepped aside and Mrs. Walters saw her baby had no stomach, as if it had been eaten out, and the little body had let its blood out all over the floor.

"Oh, God," sobbed Mrs. Walters. "No. No. No. No."

She reached out for the loose head of her baby but she could not keep her balance while kneeling and slipped again.

The ambulance that was supposed to have taken Dr. Feinberg to the hospital was found with its front twisted around a tree trunk on Storrow Drive. One driver dead with his throat torn out and the other babbling.

Detectives pieced together that the last passenger was Dr. Feinberg. She had been in a coma, but now she was not in the wrecked ambulance. Whoever had killed the driver had taken her. There was blood in the front seat. There was no blood in the back. The attendant who lived had a single deep gash near his forehead.

The forensic surgeon asked if they were going to return the attendant to the zoo. He said the attendant should go back because if he carried that fear of animals with him for long, the animals would know it.

"He'd better go back tomorrow or he'll never go back at all. He'll be too afraid. That's what I'm saying. I've treated claw wounds before," the surgeon said.

"He didn't work in no zoo," said the detective. "He was an ambulance attendant who was knifed. He didn't work in no zoo."

"That on the head is a claw mark," said the doctor. "No knife cuts like that. A knife doesn't rip like that. That's puncture, then rip."

When the corpse of baby Ethel came in on another case, the doctor was sure there was a big cat loose in the city.

"Look at the belly," he said.