Susan gave him a frown. “Okay, try this one . . .‘kitchen.’ ”

He didn’t hesitate. “Bedroom.”

Susan arched her eyebrows coyly. “Okay, how about this . .. ‘cat.’ ”

“Gut,” Becker fired back.

“Gut?”

“Yeah. Catgut. Squash racquet string of champions.”

“That’s pleasant.” She groaned.

“Your diagnosis?” Becker inquired.

Susan thought a minute. “You’re a childish, sexually frustrated squash fiend.”

Becker shrugged. “Sounds about right.”

It went on like that for weeks. Over dessert at all-night diners Becker would ask endless questions.

Where had she learned mathematics?

How did she end up at the NSA?

How did she get so captivating?

Susan blushed and admitted she’d been a late bloomer. Lanky and awkward with braces through her late teens, Susan said her Aunt Clara had once told her God’s apology for Susan’s plainness was to give her brains. A premature apology, Becker thought.

Susan explained that her interest in cryptography had started in junior high school. The president of the computer club, a towering eighth grader named Frank Gutmann, typed her a love poem and encrypted it with a number-substitution scheme. Susan begged to know what it said. Frank flirtatiously refused. Susan took the code home and stayed up all night with a flashlight under her covers until she figured out the secret—every number represented a letter. She carefully deciphered the code and watched in wonder as the seemingly random digits turned magically into beautiful poetry. In that instant, she knew she’d fallen in love—codes and cryptography would become her life.

Almost twenty years later, after getting her master’s in mathematics from Johns Hopkins and studying number theory on a full scholarship from MIT, she submitted her doctoral thesis, Cryptographic Methods, Protocols, and Algorithms for Manual Applications. Apparently her professor was not the only one who read it; shortly afterward, Susan received a phone call and a plane ticket from the NSA.

Everyone in cryptography knew about the NSA; it was home to the best cryptographic minds on the planet. Each spring, as the private-sector firms descended on the brightest new minds in the workforce and offered obscene salaries and stock options, the NSA watched carefully, selected their targets, and then simply stepped in and doubled the best standing offer. What the NSA wanted, the NSA bought. Trembling with anticipation, Susan flew to Washington’s Dulles International Airport where she was met by an NSA driver, who whisked her off to Fort Meade.

There were forty-one others who had received the same phone call that year. At twenty-eight, Susan was the youngest. She was also the only female. The visit turned out to be more of a public relations bonanza and a barrage of intelligence testing than an informational session. In the week that followed, Susan and six others where invited back. Although hesitant, Susan returned. The group was immediately separated. They underwent individual polygraph tests, background searches, handwriting analyses, and endless hours of interviews, including taped inquiries into their sexual orientations and practices. When the interviewer asked Susan if she’d ever engaged in sex with animals, she almost walked out, but somehow the mystery carried her through—the prospect of working on the cutting edge of code theory, entering “The Puzzle Palace,” and becoming a member of the most secretive club in the world—the National Security Agency.

Becker sat riveted by her stories. “They actually asked you if you’d had sex with animals?”

Susan shrugged. “Part of the routine background check.”

“Well . . .” Becker fought off a grin. “What did you say?”

She kicked him under the table. “I told them no!” Then she added, “And until last night, it was true.”

In Susan’s eyes, David was as close to perfect as she could imagine. He only had one unfortunate quality; every time they went out, he insisted on picking up the check. Susan hated seeing him lay down a full day’s salary on dinner for two, but Becker was immovable. Susan learned not to protest, but it still bothered her. I make more money than I know what to do with, she thought. I should be paying.

Nonetheless, Susan decided that aside from David’s outdated sense of chivalry, he was ideal. He was compassionate, smart, funny, and best of all, he had a sincere interest in her work. Whether it was during trips to the Smithsonian, bike rides, or burning spaghetti in Susan’s kitchen, David was perpetually curious. Susan answered what questions she could and gave David the general, unclassified overview of the National Security Agency. What David heard enthralled him.

Founded by President Truman at 12:01 a.m. on November 4, 1952,the NSA had been the most clandestine intelligence agency in the world for almost fifty years. The NSA’s seven-page inception doctrine laid out a very concise agenda: to protect U.S. government communications and to intercept the communications of foreign powers.

The roof of the NSA’s main operations building was littered with over five hundred antennas, including two large radomes that looked like enormous golf balls. The building itself was mammoth—over two million square feet, twice the size of CIA headquarters. Inside were eight million feet of telephone wire and eighty thousand square feet of permanently sealed windows.

Susan told David about COMINT, the agency’s global reconnaissance division—a mind-boggling collection of listening posts, satellites, spies, and wiretaps around the globe. Thousands of communiqués and conversations were intercepted every day, and they were all sent to the NSA’s analysts for decryption. The FBI, CIA, and U.S. foreign policy advisors all depended on the NSA’s intelligence to make their decisions.

Becker was mesmerized. “And code-breaking? Where do you fit in?”

Susan explained how the intercepted transmissions often originated from dangerous governments, hostile factions, and terrorist groups, many of whom were inside U.S. borders. Their communications were usually encoded for secrecy in case they ended up in the wrong hands—which, thanks to COMINT, they usually did. Susan told David her job was to study the codes, break them by hand, and furnish the NSA with the deciphered messages. This was not entirely true.

Susan felt a pang of guilt over lying to her new love, but she had no choice. A few years ago it would have been accurate, but things had changed at the NSA. The whole world of cryptography had changed. Susan’s new duties were classified, even to many in the highest echelons of power.

“Codes,” Becker said, fascinated. “How do you know where to start? I mean . . . how do you break them?”

Susan smiled. “You of all people should know. It’s like studying a foreign language. At first the text looks like gibberish, but as you learn the rules defining its structure, you can start to extract meaning.”

Becker nodded, impressed. He wanted to know more.

With Merlutti’s napkins and concert programs as her chalkboard, Susan set out to give her charming new pedagogue a mini course in cryptography. She began with Julius Caesar’s “perfect square” cipher box.

Caesar, she explained, was the first code-writer in history. When his foot-messengers started getting ambushed and his secret communiqués stolen, he devised a rudimentary way to encrypt his directives. He rearranged the text of his messages such that the correspondence looked senseless. Of course, it was not. Each message always had a letter-count that was a perfect square—sixteen, twenty-five, one hundred—depending on how much Caesar needed to say. He secretly informed his officers that when a random message arrived, they should transcribe the text into a square grid. If they did, and read top-to-bottom, a secret message would magically appear.

Over time Caesar’s concept of rearranging text was adopted by others and modified to become more difficult to break. The pinnacle of non computer-based encryption came during World War II. The Nazis built a baffling encryption machine named Enigma. The device resembled an old-fashioned typewriter with brass interlocking rotos that revolved in intricate ways and shuffled cleartext into confounding arrays of seemingly senseless character groupings. Only by having another Enigma machine, calibrated the exact same way, could the recipient break the code.

Becker listened, spellbound. The teacher had become the student.

One night, at a university performance of The Nutcracker, Susan gave David his first basic code to break. He sat through the entire intermission, pen in hand, puzzling over the eleven-letter message:

HL FKZC VD LDS

Finally, just as the lights dimmed for the second half, he got it. To encode, Susan had simply replaced each letter of her message with the letter preceding it in the alphabet. To decrypt the code, all Becker had to do was shift each letter one space forward in the alphabet—“A” became “B,” “B” became “C,” and so on. He quickly shifted the remaining letters. He never imagined four little syllables could make him so happy:

IM GLAD WE MET

He quickly scrawled his response and handed it to her:

ID SNN

Susan read it and beamed.

Becker had to laugh; he was thirty-five years-old, and his heart was doing back flips. He’d never been so attracted to a woman in his life. Her delicate European features and soft brown eyes reminded him of an ad for Estée Lauder. If Susan’s body had been lanky and awkward as a teenager, it sure wasn’t now. Somewhere along the way, she had developed a willowy grace—slender and tall with full, firm breasts and a perfectly flat abdomen. David often joked that she was the first swimsuit model he’d ever met with a doctorate in applied mathematics and number theory. As the months passed, they both started to suspect they’d found something that could last a lifetime.

They’d been together almost two years when, out of the blue, David proposed to her. It was on a weekend trip to the Smoky Mountains. They were lying on a big canopy bed at Stone Manor. He had no ring—he just blurted it out. That’s what she loved about him—he was so spontaneous. She kissed him long and hard. He took her in his arms and slipped off her nightgown.

“I’ll take that as a yes,” he said, and they made love all night by the warmth of the fire.

That magical evening had been six months ago—before David’s unexpected promotion to chairman of the Modern Language Department. Their relationship had been in a downhill slide ever since.