A/N: Contains spoilers for "The Fourth Horseman" and "Ripple Effect."

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"Unscheduled offworld activation," Sergeant Walter Harriman announced. Probably SG-1. It was usually SG-1. Always off on other planets, having adventures. He didn't mind it so much, though. "Chevron One" et cetera grew a little boring after a while. The occasional unscheduled incoming wormhole brought a little variety to his life.

General Landry descended the stairs into the Control Room. "SG-1?" he asked.

Walter shook his head. "They're not due for another hour, sir. There's no IDC coming through yet." Perhaps it was an alien attack, then. Not that SG-1 didn't thwart at least a dozen of those a week.

The iris deactivation code came up on his screen. "It's coming through now, sir."

"Who is it?" General Landry asked.

Walter stared at the name that popped up. It was impossible. It didn't make any sense.

"Walter?"

"It's me, sir," he said.

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"How is that possible?" asked Landry.

"I don't know, sir," said Walter. "I've never even used my code." All personnel were assigned them, just in case, but he'd never gone through the Gate. "Should I open the iris?"

"Go ahead, Walter."

General Landry spoke into the microphone to the Gate Room. "Defense team, stand by." Obviously curiosity was getting the better of the General, too.

Walter pressed his palm to the lock. The iris opened. The defense team stood ready to shoot whatever appeared. Curiosity was hardly a sufficient excuse for a foothold, after all.

But the figure that came through the Gate was neither alien nor hostile-looking. He was clad in green BDUs and his face sported a few days' growth of graying beard. A pair of glasses was perched atop his bald head. He looked around the Gate Room, then pushed the glasses down to a more useful position and took another glance.

Walter stared. It was him.

"What's going on?" the doppelganger asked.

"Walter?" General Landry echoed the question.

"I have no idea, sir. I – " He pointed to the computer screen. "That's my code. But I don't know how anyone could have gotten it. Unless – "

Unless they were from an alternate universe. They'd had visitors like that before. The Gate wasn't intended to do that; but it wasn't intended for time travel, either, and SG-1 had done that. Maybe in another universe he was more than just a Gate technician. Maybe –

"Sergeant Harriman?" Landry called down to the Gate Room.

The alternate Walter looked up, and shock registered on his face. "General Landry," he said. "You're alive? The plague – "

And then he caught sight of his alternate self. Their eyes met. It was disorienting, looking into a mirror that wasn't quite right. But more than anything, it was exciting.

"Take him to a holding room," Landry instructed the team.

"General, what's going on here?" Walter's double demanded. "Why am I – Where is this place?"

"We'll try to answer your questions, Sergeant, just as soon as we know the answers ourselves."

"Sir?" said Walter. "Maybe I can help you with that."

"I hope so, Walter," General Landry said.

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Walter sat down across the table from his double. "The DNA test confirmed that you are Sergeant Walter Harriman," he said. He liked saying it. It made him feel important. And suddenly he was.

His alternate self shook his head. "But I can't be Walter Harriman, because you are, right?"

"You can be. Just not the one from this universe."

"How is that possible? I mean, I might not be experienced at the whole going offworld thing, but I know that isn't how the Gate works." He pushed his glasses up his forehead and pinched the bridge of his nose. "This sounds like something that would happen to SG-1."

It did, Walter thought. But it wasn't happening to SG-1. It was happening to him.

"What do I – you – do in your universe?" Walter asked.

"I used to be a Gate technician," his double began. "But then the Ori sent the plague. You do know about the Ori here?"

"We've had some dealings with them, yes," Walter said carefully. General Landry had instructed him not to reveal too much, just in case this was some sort of trick. But Walter didn't see how it could be. None of their alien enemies would have had any access to his DNA or memories. And they certainly wouldn't know enough about the SGC's interaction with alternate universes to set up this elaborate scenario.

"It spread too quickly for us to control. The offworld teams were the first to contract it. Over half of the SGC personnel are either dead or dying, and it's already spread outside the base. A few of us seemed to show some resistance to the virus. Colonel Carter formed new teams and sent us out to search for a cure."

"Colonel Carter?"

"She took command of the SGC after General Landry's death."

Half the SGC dead. Even though it had happened in another universe, the thought hit Walter hard. He'd wanted to go through the Stargate, but not like this.

"You have to help us get back," the alternate Walter said. "We have to keep looking for a cure. We might not be much, but we're all Earth has left."

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Walter had just finished relaying the content of the interview to General Landry when Colonel Mitchell strode into the Conference Room.

"So, Walter," said Mitchell as he clapped the technician on the back. "I hear you're Earth's last, best hope."

Walter flushed. He hadn't realized that Mitchell knew his name. "Not exactly, sir."

"Our visitor from another universe is looking for a cure to the Prior's plague," said General Landry.

"We can help them with that, can't we, sir?" asked Mitchell.

Landry nodded. "We need to reproduce the antibody we generated from Orlin's formula."

"I'll get Colonel Carter right on it," Mitchell said. He was about to leave the conference room when the klaxons blared to life.

"Unscheduled offworld activation!" came the voice of the technician on duty.

"Not again," said Landry, and headed for the stairs, Mitchell and Walter close behind. It was strange for Walter to watch as the technician waited for some sign of who was beyond the wormhole. Usually he was the one behind the computer.

"Receiving IDC, sir," the technician said. "It's – " he turned around to look at Walter. "It's Sergeant Harriman."

General Landry raised his eyebrows. "Another one?" he asked.

So he got to go through the Gate in every universe except for this one?

"Open the iris," said the General. The technician complied, and a few moments later there was another Walter standing on the ramp, looking puzzled as the wormhole closed behind him. This one had no glasses and was sporting desert camouflage.

"Take him to interrogation room three," General Landry instructed the defense team. He turned to Walter. "We're going to need your help again, Sergeant."

Walter smiled. "My pleasure, sir."

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Much to his dismay, Walter discovered that his new alternate self had a bit of an attitude problem. Much to his excitement, he also discovered that Lieutenant Harriman was a member of SG-23. His team, too, was actively searching for a cure for the Ori plague.

A fact which his counterpart saw it fit to rearticulate as often as possible. Walter had barely gotten through the explanation about alternate universes when his alternate self demanded that he explain why, if they already knew how he got there, they were talking to him instead of figuring out a way to get him back home. His Earth was dying, after all.

"The fact is, we're not sure how you got here," Walter said. "The Gate isn't meant for travel between universes, but somehow it's happened twice in one ay. Once we figure out what went wrong, we'll hopefully be able to get everyone home."

"I hope so, Sergeant." He sneered at the last word, as if satisfied that his life in his own universe was superior to Walter's. Walter didn't ask if he'd ever been a Gate technician. He figured it wouldn't be a pleasant conversation to have. He was about to ask more about the plague when the technician's voice came over the speaker:

"Unscheduled offworld activation!"

Probably just an SG team coming in hot. No reason for a third alternate version of himself to come through the Gate now.

Except that the next announcement was, "Sergeant Harriman to the Control Room."

This was not a good sign.

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"That's seventeen versions of Sergeant Harriman so far," said General Landry.

Well, not exactly correct, Walter thought. They weren't all Sergeant Harriman. He'd been a Lieutenant, a civilian scientist – and in the last alternate universe, the leader of SG-1. Could he really have been a Colonel? Were the changes in the other universes results of something he had done, or of circumstances beyond his control? He wasn't sure if he should be awed at what he had accomplished in other universes, or ashamed that he hadn't made the same accomplishments in this one.

"We're working on a solution, sir," said Colonel Carter. "But frankly, I'm not sure what might have caused this."

"Wait a minute," said Walter. If they saw where the wormhole had originated... He brought up the record of recent incoming Gate travel. "Aha!" He pointed to the screen. "PX7-455."

"Carter leaned forward. "That's the planet – "

"On the other side of a black hole," Walter finished. "If the wormhole went through the black hole..."

"...it could have caused a transdimensional rift." Carter scrolled through the other Gate addresses. "You're absolutely right. All of the teams gated in from planets in that sector of space. If we could reverse whatever has been done to the black hole, we'll be able to stop the problem."

"What about getting them back to their universes?" Landry asked.

"I don't know," said Carter. "There might not be a way to reverse the damage without sealing off the rift altogether."

"We have to get them back," said Walter. "We have the cure to the plague. We can help all of them."

Maybe, he thought, for some universe, this Watler Harriman really was Earth's last, best hope.

Carter nodded. "I'll see what I can do."

As she stood up to leave, the Gate came to life again. "Unscheduled offworld activation!" Walter announced. "Receiving IDC."

It was himself. Again.

But the figure who emerged from the wormhole was barely recognizable. He was dignified-looking, with a full beard, and... were those stars on his dress uniform?

"Identify yourself!" General Landry said, apparently not recognizing him either.

"General Walter Harriman, returning from treaty negotiations on P4R-787. Who are you?"

"General?" said Carter.

"General!" Walter repeated.

"General, we're ready to go," said Colonel Mitchell.

"All right, Walter, dial the Gate. Walter?"

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Walter woke with a start. His glasses fell from their awkward perch on his forehead.

"Sorry, sir," he said. "Must've dozed off there for a minute."

"Well, if you're awake, SG-1 has figured out how to return their counterparts to their respective universes."

"Yes, sir." SG-1 had saved the day. They always did. Walter typed in the coordinates. "Chevron One encoded!"

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- finis -