“Something to do with the saints, I guess.”

Suddenly Tom gasped.

“I know.” He sprang from his chair, sending Bridget flapping away to safety. “I know! I know!”

“Where is it?” Sally said.

“Erkenwald!”

She looked confused. “Where?”

“Not where. Who. Saint Erkenwald. He’s a patron saint of London. Reverend Wright talked about him at service last year. Or maybe two years ago. When he was telling us how we should make a pilgrimage. Do you remember?”

“Er…” I didn’t recall this at all. But then my mind usually drifted during Reverend Wright’s sermons.

“He told us about Saint Erkenwald,” Tom insisted, “and about how people would make pilgrimages to London to visit his tomb.”

“But where is his tomb?” Sally said.

“In the ‘hallowed halls’ of Saint Paul’s Cathedral! Do you see? It fits. Visit them—the saints, Paul and Erkenwald—in the cathedral, and pray upon his grave. That’s Erkenwald’s tomb!”

That made perfect sense. I looked up at him, amazed.

“I got it! I got it!” Tom marched around the room. “Look at me, I’m a spy, too.” He hid behind the doorjamb, peeking his head out.

Sally giggled.

“Told you the hat makes me smarter,” he said.

“I suppose it does,” I said, trying not to laugh. “We’ll go to Saint Paul’s, then. But leave the hat behind for this one.”

He clutched it to his chest. “What? Why?”

“Because if we’re going to another letter drop, I want to be quiet about it. And that hat… isn’t.”

Disappointed, Tom left it on Isaac’s table, commiserating with Sally. “He just doesn’t understand fashion.”

“I know,” she said sympathetically. I couldn’t tell if she was humoring him, or whether I should actually be offended.

We hurried away, getting halfway down the steps before remembering Isaac wouldn’t be hurrying anywhere. He leaned on Sally to help him navigate the stairs again, going even more slowly down than up.

“Take this.” Isaac reached under his shirt and removed his key, hanging from a string around his neck. He shuffled toward the back of his counter, and, with some effort, pulled on the book that cracked the bookcase open, leading to the secret library downstairs.

Sally lingered, watching him. As I unlocked the front door, she put a hand on my arm, speaking quietly. “I’m going to stay.”

“You are? Why?”

“How many stairs did you say it was down to the library?”

I looked over at Isaac. With difficulty, he heaved the bookcase open.

Too many, I thought.

“He needs help, Christopher,” Sally said. “I can help. I want to.”

“We’ll all stay,” Tom said.

Sally shook her head. “Christopher has to finish this puzzle. And you have to be there in case anything goes wrong. Give me Bridget. I’ll stay here and search the library, find out what Isaac has about the Templars. It’ll be faster for everyone.”

She had said she wanted to be useful. “All right,” I said, handing her my pigeon. “Saint Paul’s is just up the street. We’ll hurry back.”