“I've found that few things are coincidental,” Austin said. “However, it's a coincidence that I'm still thirsty and there's an untouched beer on the table.”

“I'm too cranked up to drink.” Barrett shoved the beer across to Austin, who shared half of it with Karla.

“We were talking about coincidences,” Austin said.

Barrett nodded. “Kovacs was an amateur cryptologist. I started with the premise that the rhyme might be a cipher. I guessed that the topsy-turvy couplets were simply 'nulls'—letters or words placed in a cipher to confuse—so I put them aside and stuck with the main body of the verse. A cipher is different from a code, which usually requires a codebook to make the translation. To unlock a cipher, you have to have a key, which is included in the message itself. One phrase jumped out immediately.”

“The key is in the door,” Karla said without thinking.

“That's the one! It seemed obvious, almost too obvious,” Barrett said, “but Kovacs was a scientist who would have been obsessed with precision. It would have been more precise for him to have said that the key is in the lock.”

“The key was in the word door itself,” Austin said.

“That was my thinking,” Barrett said. “Door became my key word. You have to look at code breaking in a couple of ways. At one level, you're dealing with the mechanics of things, such as word or letter transpositions and substitutions. At another level, you're looking at the meaning of things.” Seeing his explanation greeted with blank looks, he said, “What does a door do?”

“That's easy,” Karla said. “It separates one room from another. You have to open and close it to pass through.”

“Correct,” Barrett said. “The word's opening letter is D.”

He grabbed a clean napkin and with his ballpoint pen wrote:

DEFGHIJKLMNOPQRSTUVWXYZ

ABC

“This sets the pattern of letters for the plain alphabet. I took the last letter in door and used it in the same configuration for the cipher alphabet.”

“Let me try,” Karla said. Taking the pen, she wrote:

RSTUVWXYZABCDEFGHIJKLMN

OPQ

“I'm buying you a ticket to Bletchley Park,” Barrett said, referring to the British code-breaking headquarters during World War II.

“Using the alphabets to write the word message, you'd still get gibberish.” Karla stared at the word with disappointment in her eyes.