She led him into an anteroom that resembled a small cage. One door of the cage permitted access to a staircase that went down to the cellar. Another door led to the convent’s chapel and living quarters.

“I’m Sister Ann.” The nun wore old-fashioned gold-rimmed spectacles. Her face, framed by the black wimple, was smooth and strong and almost ageless. “I’ve got relatives in Chicago,” she said. “Are you from Chicago?”

“No. Sorry.” Gabriel touched the iron bars that surrounded them.

“We are cloistered Benedictines,” Sister Ann explained. “That means we spend our time in prayer and contemplation. There are always two sisters who deal with the public. I’m the permanent one, and then we rotate in another every month or so.”

Gabriel nodded politely, as if this were useful information. He wondered how he was going to ask about his father.

“I’d take you down to the crypt, but I’ve got to balance the accounts.” Sister Ann pulled a large key ring out of her pocket and unlocked one of the gates. “Wait here. I’ll get Sister Bridget.”

The nun vanished down a corridor, leaving Gabriel alone within the cage. There was a rack of religious pamphlets on the wall and an appeal for money on the bulletin board. Apparently, some bureaucrat working for the City of London had decided that the nuns had to spend three hundred thousand pounds to make the convent wheelchair accessible.

Gabriel heard the rustle of fabric and then Sister Bridget appeared to float down the hallway to the iron bars. She was much younger than Sister Ann. The Benedictine habit concealed everything but her plump cheeks and dark brown eyes.

“You’re an American.” Sister Bridget had a light, almost breathless way of speaking. “We get a lot of Americans here. They usually make very nice donations.”

Sister Bridget entered the cage and unlocked the second door. As Gabriel followed the nun down a winding metal staircase, he learned that hundreds of Catholics had been hung or beheaded at Tyburn gallows right up the street. During Elizabethan times there seemed to be some form of diplomatic immunity, because the Spanish ambassador was allowed to attend these executions and carry away locks of hair from the dead. More relics had appeared in modern times, when the gallows area was dug up to create a roundabout.

The crypt resembled a large basement in an industrial building. It had a black concrete floor and a white vaulted ceiling. Someone had built glass cases to display bone fragments and pieces of bloodstained clothing. There was even a framed prison letter scrawled by one of the martyrs.

“So they were all Catholics?” Gabriel asked. He stared at a yellowed leg bone and two ribs.

“Yes. Catholic.”

Gabriel glanced at the nun’s face and realized that she was lying. Disturbed by this sin, she struggled with her conscience for a moment, and then said cautiously, “Catholics and…a few others.”

“You mean Travelers?”

She looked startled. “I don’t know what you’re talking about.”

“I’m looking for my father.”

The nun gave him a sympathetic smile. “Is he in London?”

“My father is Matthew Corrigan. I think he sent a letter from this place.”

Sister Bridget’s right hand came up to her breast as if to ward off a blow. “Men aren’t allowed in this convent.”

“My father is hiding from people who want to hurt him.”

The nun’s anxiety was transformed into panic. She stumbled backward, moving toward the staircase. “Matthew told us he was going to leave a sign here in the crypt. That’s all I can tell you.”

“I’ve got to find him,” Gabriel said. “Please tell me where he is.”

“I’m sorry, I can’t say more,” the nun whispered. And then she was gone, her heavy shoes clomping up the metal stairs.

Gabriel circled the crypt like a man trapped in a building about to collapse. Bones. Saints. A bloodstained shirt. How would this lead him to his father?

Footsteps on the staircase. He expected to see Sister Bridget return, but it was Sister Ann. The Irish nun looked angry. Reflected light flashed on the surface of her glasses.

“May I help you, young man?”

“Yes. I’m looking for my father, Matthew Corrigan. And the other nun, Sister Bridget, told me-”

“That’s enough. You have to leave.”

“She said he left a sign-”

“Leave immediately. Or I will call the police.”

The expression on the elderly nun’s face allowed no objection. The keys on her iron ring made a bright jingling sound as she followed Gabriel up the staircase and then out of the convent. He stood in the cold as Sister Ann began to shut the door.

“Sister, please. You have to understand-”

“We know what happened in America. I read in the newspaper how those people were killed. Children, too. They didn’t even spare the little ones. We won’t have such things here!”

She shut the door-hard-and Gabriel heard the sounds of locks being snapped shut. He felt like shouting and pounding on the door, but that would just bring the police. Not knowing what to do, the Traveler gazed out at the traffic and the bare trees of Hyde Park. He was in a strange city without money or friends, and no one was going to defend him from the Tabula. He was alone, truly alone, within the invisible prison.

After wandering aimlessly for a few hours, Gabriel found his way to an Internet café on Goodge Street near the University of London. The café was run by a group of amiable Koreans who spoke only a few words of English. Gabriel got a payment card and walked by a row of computers. Some people were looking at pornography, while others were buying cheap plane tickets. The blond teenager sitting at the computer next to him was playing an online game where his avatar would hide in a building and kill any stranger who showed up alone.

Gabriel sat at a computer and entered different chat rooms trying to find Linden, the French Harlequin who had sent money to New York. After two hours of failure, he left a message on a Web site for collectors of antique swords. G. in London. Needs financing. He paid the Koreans for his computer time and spent the rest of the day in the library reading room at the University of London. When the library closed at seven o’clock, he returned to the Internet café and discovered that no one had responded to his message. Back out on the street, it was cold enough to see his breath. A group of students brushed past him, laughing about something. He had less than ten pounds in his pocket.

It was too cold to sleep outside, and there were surveillance cameras on the underground. As he drifted down Tottenham Court Road past brightly lit shops selling televisions and computers, he remembered Maya telling him about a location in West Smithfield where heretics, rebels, and Harlequins were executed by authorities. Once she used her father’s language when she mentioned the area, calling it Blutacker. The German word originally denoted the cemetery near Jerusalem bought with the silver given to Judas, and then it acquired a more general meaning. It was any accursed place-blood ground. If this really was a Harlequin site, then perhaps there was a message board in the area or some indication of where he could find help.

He headed toward East London, asking for directions from people who all seemed to be either drunk or lost. One man who could barely walk straight started waving his arms around as if he were swatting flies. Finally, Gabriel walked up Giltspur Street past St. Bartholomew’s Hospital and found two memorials that were only a few feet apart. One was in memory of the Scottish rebel William Wallace, while the other plaque was placed a few feet away from where the Crown had burned Catholics at the stake. Blutacker, thought Gabriel. But there were no Harlequin signs anywhere.