Page 40 of The Secret of Secrets

Unfortunately, the decimal point in 3.14159 was problematic. First, there were no decimal points in a pure alphanumeric passcode. And second, the decimal point was not an Arabic creation; it was invented by a Scottish mathematician, John Napier.

You can solve both problems simply by deleting the decimal point.

There was only one problem: the number 314159 represented pi…not PSI.

And it’s still missing the “little Latin twist.”

Ten minutes later, Langdon had made no further progress, and he decided he too should probably call it a night. Gessner’s passcode can wait…or better yet, be forgotten.

Langdon climbed into bed beside Katherine, where he slept soundly for several hours…until she woke up screaming from her nightmare.

A lifetime ago, Langdon thought, now standing in the darkened elevator alcove, staring at the numeric keypad and wishing he’d solved Gessner’s annoying little riddle.

On the other side of the wall, Pavel cursed loudly, and Langdon heard him dash out of the atrium, probably to go find Janáček. Langdon knew this moment might be an opportunity to slip out of the bastion unseen…but to where?

I’m not leaving without Katherine, he thought, increasingly fearful that something might have happened to her. I need to get downstairs.

He looked back at the keypad, wondering if he might have a better chance of deciphering the final piece of Gessner’s passcode now that an evening had passed. After all, there was a reason we “slept on” our problems; the subconscious mind could make remarkable connections while we slept.

Langdon had gone to bed last night thinking the number 314159 was an accurate representation of “an Arabic tribute to an ancient Greek.”

Still, it was not quite right.

I’m missing the Latin twist.

Langdon knew the majority of languages in the world—including English—used the lettering system known as the Roman or Latin alphabet. As he surveyed the numbers and letters on the buttons of the keypad, he realized he had become so focused on numbers that he’d forgotten he could also use letters.

Is the “Latin twist” a letter?

As he considered it, the simplest of shapes materialized in his mind—the twisting curve of the letter S.

My God, he realized. A literal “Latin twist”!

In that moment, he flashed on Gessner smugly dropping her lemon twist into the center of her drink, and he couldn’t help but be a little impressed.

“S” is the missing piece of the puzzle.

The rest was simple.

PI becomes PSI!

Gessner’s code was a mixture of Arabic and Latin symbols—numbers and letters—and if Langdon was not mistaken, the solution had to be 314S159!

He rechecked the logic against what Gessner had said. “An Arabic tribute to an ancient Greek with a Latin twist.”

The number 314159 is a purely Arabic tribute…to the Greek number pi…and the “S” in the middle is a Latin twist that turns PI…into PSI…which Gessner said was her passcode.

If there had ever been a moment to shout Archimedes’s exclamation “Eureka!” this was it, but instead Langdon moved silently to the keypad.

Holding his breath, he carefully entered seven characters into the digital screen.

3 1 4 S 1 5 9

After double-checking the sequence, he exhaled and pressed Enter.

Nothing happened.

An immediate rush of despair washed over him, but a moment later Langdon heard a click and a faint mechanical whir behind the door. The sound grew louder…an elevator ascending.