"Manual abort?" Susan stared at her screen, mystified.

She knew she hadn't typed any manual abort command-at least not intentionally. She wondered if maybe she'd hit the wrong sequence of keys by mistake.

"Impossible," she muttered. According to the headers, the abort command had been sent less than twenty minutes ago. Susan knew the only thing she'd typed in the last twenty minutes washer privacy code when she'd stepped out to talk to the commander. It was absurd to think the privacy code could have been misinterpreted as an abort command.

Knowing it was a waste of time, Susan pulled up her ScreenLock log and double-checked that her privacy code had been entered properly. Sure enough, it had.

"Then where," she demanded angrily, "where did it get a manual abort?"

Susan scowled and closed the ScreenLock window. Unexpectedly, however, in the split second as the window blipped away, something caught her eye. She reopened the window and studied the data. It made no sense. There was a proper "locking" entry when she'd left Node 3, but the timing of the subsequent "unlock" entry seemed strange. The two entries were less than one minute apart. Susan was certain she'd been outside with the commander for more than one minute.

Susan scrolled down the page. What she saw left her aghast. Registering three minutes later, a second set of lock-unlock entries appeared. According to the log, someone had unlocked her terminal while she was gone.

"Not possible!" she choked. The only candidate was Greg Hale, and Susan was quite certain she'd never given Hale her privacy code. Following good cryptographic procedure, Susan had chosen her code at random and never written it down; Hale's guessing the correct five-character alphanumeric was out of the question-it was thirty-six to the fifth power, over sixty million possibilities.

But the ScreenLock entries were as clear as day. Susan stared at them in wonder. Hale had somehow been on her terminal while she was gone. He had sent her tracer a manual abort command.

The questions of how quickly gave way to questions of why? Hale had no motive to break into her terminal. He didn't even know Susan was running a tracer. Even if he did know, Susan thought, why would he object to her tracking some guy named North Dakota?

The unanswered questions seemed to be multiplying in her head. "First things first," she said aloud. She would deal with Hale in a moment. Focusing on the matter at hand, Susan reloaded her tracer and hit the enter key. Her terminal beeped once.

TRACER SENT

Susan knew the tracer would take hours to return. She cursed Hale, wondering how in the world he'd gotten her privacy code, wondering what interest he had in her tracer.

Susan stood up and strode immediately for Hale's terminal. The screen was black, but she could tell it was not locked-the monitor was glowing faintly around the edges. Cryptographers seldom locked their terminals except when they left Node 3 for the night. Instead, they simply dimmed the brightness on their monitors-a universal, honor-code indication that no one should disturb the terminal.

Susan reached for Hale's terminal. "Screw the honor code," she said. "What the hell are you up to?"

Throwing a quick glance out at the deserted Crypto floor, Susan turned up Hale's brightness controls. The monitor came into focus, but the screen was entirely empty. Susan frowned at the blank screen. Uncertain how to proceed, she called up a search engine and typed:

SEARCH FOR: "TRACER"

It was a long shot, but if there were any references to Susan's tracer in Hale's computer, this search would find them. It might shed some light on why Hale had manually aborted her program. Seconds later the screen refreshed.

NO MATCHES FOUND

Susan sat a moment, unsure what she was even looking for. She tried again.

SEARCH FOR: "SCREENLOCK"

The monitor refreshed and provided a handful of innocuous references-no hint that Hale had any copies of Susan's privacy code on his computer.

Susan sighed loudly. So what programs has he been using today? She went to Hale's "recent applications" menu to find the last program he had used. It was his E-mail server. Susan searched his hard drive and eventually found his E-mail folder hidden discreetly inside some other directories. She opened the folder, and additional folders appeared; it seemed Hale had numerous E-mail identities and accounts. One of them, Susan noticed with little surprise, was an anonymous account. She opened the folder, clicked one of the old, inbound messages, and read it.

She instantly stopped breathing. The message read:

TO: [email protected]

FROM: [email protected]

GREAT PROGRESS! DIGITAL FORTRESS IS ALMOST DONE.

THIS THING WILL SET THE NSA BACK DECADES!

As if in a dream, Susan read the message over and over. Then, trembling, she opened another.

TO: [email protected]

FROM: [email protected]

ROTATING CLEARTEXT WORKS! MUTATION STRINGS ARE THE TRICK!

It was unthinkable, and yet there it was. E-mail from Ensei Tankado. He had been writing to Greg Hale. They were working together. Susan went numb as the impossible truth stared up at her from the terminal.

Greg Hale is NDAKOTA?

Susan's eyes locked on the screen. Her mind searched desperately for some other explanation, but there was none. It was proof-sudden and inescapable: Tankado had used mutation strings to create a rotating cleartext function, and Hale had conspired with him to bring down the NSA.

"It's..." Susan stammered. "It's... not possible."

As if to disagree, Hale's voice echoed from the past: Tankado wrote me a few times... Strathmore took a gamble hiring me... I'm getting out of here someday.

Still, Susan could not accept what she was seeing. True, Greg Hale was obnoxious and arrogant-but he wasn't a traitor. He knew what Digital Fortress would do to the NSA; there was no way he was involved in a plot to release it!

And yet, Susan realized, there was nothing to stop him-nothing except honor and decency. She thought of the Skipjack algorithm. Greg Hale had ruined the NSA's plans once before. What would prevent him from trying again?

"But Tankado..." Susan puzzled. Why would someone as paranoid as Tankado trust someone as unreliable as Hale?

She knew that none of it mattered now. All that mattered was getting to Strathmore. By some ironic stroke of fate, Tankado's partner was right there under their noses. She wondered if Hale knew yet that Ensei Tankado was dead.

She quickly began closing Hale's E-mail files in order to leave the terminal exactly as she had found it. Hale could suspect nothing-not yet. The Digital Fortress pass-key, she realized in amazement, was probably hidden somewhere inside that very computer.

But as Susan closed the last of the files, a shadow passed outside the Node 3 window. Her gaze shot up, and she saw Greg Hale approaching. Her adrenaline surged. He was almost to the doors.

"Damn!" she cursed, eyeing the distance back to her seat. She knew she'd never make it. Hale was almost there.

She wheeled desperately, searching Node 3 for options. The doors behind her clicked. Then they engaged. Susan felt instinct takeover. Digging her shoes into the carpet, she accelerated in long, reaching strides toward the pantry. As the doors hissed open, Susan slid to a stop in front of the refrigerator and yanked open the door. A glass pitcher on top tipped precariously and then rocked to a stop.

"Hungry?" Hale asked, entering Node 3 and walking toward her. His voice was calm and flirtatious. "Want to share some tofu?"

Susan exhaled and turned to face him. "No thanks," she offered. "I think I'll just-" But the words got caught in her throat. She went white.

Hale eyed her oddly. "What's wrong?"

Susan bit her lip and locked eyes with him. "Nothing, "she managed. But it was a lie. Across the room, Hale's terminal glowed brightly. She'd forgotten to dim it.