“A few years ago,” he said at last, “the don accepted a contract on a gentleman who’d stolen a great deal of money from people who don’t care to have their money stolen. The gentleman was in hiding in a city like the one in this photograph. It was an old city of faded beauty, a city of hills and streetcars.”

“What was the gentleman’s name?”

“I’d rather not say.”

“Where was he hiding?”

“I’m getting to that.”

Keller was studying the front of the ticket again. “Because this gentleman had no car, he was by necessity a dedicated user of public transport. I followed him for a week before the hit, which meant that I had to be a dedicated user of public transport, too.”

“Do you recognize the ticket, Christopher?”

“I might.”

Keller picked up Gabriel’s BlackBerry, opened Google, and typed several characters into the search box. When the results appeared, he clicked one and smiled.

“Find it?” asked Gabriel.

Keller turned the BlackBerry around so Gabriel could see the screen. On it was a complete version of the ticket he had found in the home of Maggie Donahue.

“Where’s it from?” asked Gabriel.

“A city of hills and streetcars.”

“I take it you’re not referring to San Francisco.”

“No,” said Keller. “It’s Lisbon.”

“That doesn’t prove the photo was taken there,” Gabriel said after a moment.

“Agreed,” answered Keller. “But if we can prove that Catherine Donahue was there . . .”

Gabriel said nothing.

“You didn’t happen to see her passport when you were in that house, did you?”

“No such luck.”

“Then I suppose we’ll have to think of some other way to have a look at it.”

Gabriel picked up his BlackBerry and keyed in a brief message to Graham Seymour in London, requesting information on any and all foreign travel by Catherine Donahue of 8 Stratford Gardens, Belfast, Northern Ireland. One hour later, as darkness fell hard upon the city, they had their answer.

The British Foreign and Commonwealth Office issued the passport on November 10, 2013. One week later she boarded a British Airways flight in Belfast and flew to London’s Heathrow Airport where, ninety minutes later, she transferred to a second British Airways flight, bound for Lisbon. According to Portuguese immigration authorities, she remained in the country for just three days. It was her one and only foreign trip.

“None of which proves Quinn was living there at the time,” Keller pointed out.

“Why bring her to Lisbon of all places? Why not Monaco or Cannes or St. Moritz?”

“Maybe Quinn was on a budget.”

“Or maybe he keeps an apartment there, something in a charming old building in the kind of neighborhood where no one would notice a foreigner coming and going.”

“Know any places like that?”

“I’ve spent my life living in places like that.”

Keller was silent for a moment. “What now?” he asked finally.