Title: Reverberations
Author: Zubeneschamali
Rating: T (language, violence)
Summary: When a killer that Don has been chasing for over a decade shows up in Los Angeles, the case gets a lot more complicated -- and a lot more personal. Set after Season Four.

Author's Note: I've taken some liberties with Don's professional history, but as far as I know, I haven't contradicted canon. It's told half in the present day and half in flashbacks, with timestamps to keep things straight.

Acknowledgments: Thanks as always to Lady Shelley for maintaining "Running the NUMB3RS." I'm grateful to the contributors at Wikipedia and the Washington Post who did the research so I didn't have to. And many thanks to Susan W., ritt, and Kiki for their magnificent beta reading, including characterization corrections and plot-hole patching.

Disclaimer: As if.

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Prologue
July 30, 2008

It was only the tiniest moment's distraction. Only the sound of a tree branch banging on the roof in the wind. It wouldn't have mattered if Don wasn't here on his own. It shouldn't have been enough of an opportunity for a man with one handcuff already closed over his wrist. But then, not everyone was as quick on their feet as Shaun Gillis. Or as desperate.

Don had his gun trained on the killer's back while he closed the cuff over his left wrist. At the sudden crashing noise outside, his head twitched sideways. He relaxed when he heard the wind whistling outside and the second thump of the branch.

But by then, it was too late.

The darkness outside had turned the window opposite them into a mirror. Gillis had noticed Don's head turning, and, in that instant, made his move. He twisted to his right as he rose, his unencumbered hand grabbing Don's gun and pushing it away. In the same move, he used his momentum to pull his left arm free and swing it around, the empty handcuff landing solidly against Don's temple simultaneously with the fist connecting with his jaw.

Don staggered sideways under the dual blow. His weight was still precariously balanced when Gillis completed his turn, his knee coming up sharply into Don's ribs. The knee plus a strong shove sent him crashing to the ground, landing on his back with a thump that took the air out of his lungs.

He shook his head, desperately trying to clear it from its sudden throbbing. He had just raised himself up onto one elbow when he realized how fatal his distraction was going to be.

Because in the vain attempt to break his fall, he'd dropped his weapon. And now standing over him was the wanted killer he was supposed to be arresting, pointing Don's own gun at him from not two feet away.

There was no sound for a few seconds but the panting breaths of the two combatants. "What are you waiting for?" Don finally growled. He had no illusions about what was going to happen next. He knew Gillis had probably been imagining this moment for years: the FBI agent who had tracked him across the country for over a decade was now at his mercy.

"I'm savoring the moment, Agent Eppes." Gillis's cold green eyes crinkled a little at the corners. "Like you were doing a few seconds ago. Talk about turning the tables."

Don swallowed, refusing to let any of his fear creep into his expression. Mentally, he started casting around for anything that he could use as a diversion, anything he could distract Gillis with for a split second while he pulled the backup piece out of his ankle holster. Coming up with nothing, he concentrated on looking out of the corners of his eyes without taking his gaze off the gunman, still searching for something he could throw or reach for or do anything with that might serve the same distracting function as that damn tree had.

Gillis gave that same low chuckle Don had first heard over a decade ago. "Still searching for a way out, aren't you, rookie? But I still know what I'm doing far better than you. And I know that you're out of options."

He was right. David and Colby were at least ten minutes away. There was plenty of time for Gillis to pull the trigger and then disappear into the night with one more kill completed.

"I've been waiting a long time for this," the other man said almost conversationally. He centered his aim between his target's eyes and went on, "I would have killed you the first time I had the chance if I'd known what a pain in the ass you were going to be."

Instead of replying, Don looked sharply to his right as if he had just heard something. Without turning his head, he looked to his left to see Gillis taking two cautious steps backwards before looking off in the same direction, putting himself well out of range as he did so. Don measured the distance, but quickly realized that even a sudden lunge or grab for his second weapon wouldn't get him anywhere before the other man pulled the trigger.

At this point, it didn't look like there was anything he could do before that happened.

Gillis looked back at him. "Nice try, Agent."

And suddenly Don's mouth went dry. He really was out of options. The professional killer wasn't about to allow himself to be distracted by anything he could throw at him, even something as stupid as the sound of a tree branch on the roof. The weight of the .22 at his ankle was a mocking reminder of his failure to do anything useful with his own weapon, almost like the first time he'd encountered this man. God, what a damn rookie mistake he'd made!

Unlike his early errors in judgment, the cost here was going to be much higher.

As he stared up into the barrel of his own gun, watching Gillis's finger on the trigger, his heart pounding faster and faster, he realized with overwhelming dread that it was a mistake that was going to cost him his life.