“You aren’t worried they’re going to find us?” said Patton. She knew that airline manifests and customs and immigration databases were difficult, though not impossible, to hack into, but she still worried about arriving at such a public place as Heathrow. Nemo had boarded the plane as Grigore Florinescu of Romania and would rent the car as Oliver Moores of Darlington, North Yorkshire. Patton had gotten a glimpse of the bundle of passports and other papers in the black knapsack Nemo had carried on to the plane. (“In my business you should have as many identities as possible,” he had said before zipping the bag back up.) But none of their precautions—not getting rid of Patton’s phone or using only cash or Nemo’s constantly switching identities—really made any difference. If Fritz and Franz, and whomever they worked for, knew what Patton and Nemo had found, they knew where they were going.

“They will find us,” said Nemo simply. “And if we decode this message before that happens, we’ll have a distinct advantage in our next encounter.”

“It sure would be easier to do this online,” said Patton, “but if you think whoever is after us is watching the decrypt website, then I guess we’ll have to do it the old-fashioned way.”

“And what is the old-fashioned way?”

“First we need to come up with a crib. Not so easy to do seventy years after the message was sent.”

“A crib?”

“It’s a guess at a piece of decoded text. Lots of German messages began with the weather or ended with ‘Heil Hitler’—others were a lot harder to guess a crib for.”

“So how do we even start?”

“Let me have that paper,” said Patton. Nemo passed it from his cubicle to hers. “OK, we know some things about this message. According to the letterhead, it was received by someone in the H-Sonderkommando division of the SS. I have no idea what that is, and you won’t let me go online to find out, but it’s something. We also know it was probably received at Dachau on the day the Americans liberated the camp. That’s April 29, 1945. I learned that from Jasper. He was there.”

“But couldn’t Jasper have picked it up anytime?”

“He told me the only time he ever watched a German die up close was when he shot a boy in an SS uniform just outside the gates of Dachau. It haunted him—he was obsessed with everything to do with that day. I think that’s why he wanted to crack this code.”

“Why didn’t he just go online and do it like you said?”

“Well, first of all, who knows when he started working on it. It could have been decades ago when there was no Internet. And secondly, I couldn’t even get Jasper to use email or a cell phone. He was a major technophobe.”