Disclaimer: I don't own Janeway (or her crew), Sisko (or his crew), Picard (or his crew), Kirk (or his crew, sadly), and Archer (or his crew). Paramount hogs them. Though, the Xenonians and the Ambassador's species are mine.
WORK IN PROGRESS: Updates will probably be far between! (A week or two, anyway.)
I'm trying to make this story as plausible as possible. I'm gonna have to do research on black holes and wormhole theories to make this realistic, though some parts will still be raw from my imagination.
Archer knew this place. It was familiar somehow, like an old memory tickling the corners of his mind. It looked like a palace, but he knew it wasn't. A fuzzy, dreamlike haze surrounded everything, playing tricks with the corners of his vision. His shoes made an echo whenever he stepped on the shining marble floor, and chandeliers hung down from the ceiling like giant spiders hanging by a thread. The light from the antique chandeliers lit up the palace-like hall as well as a sun in a cloudless afternoon sky, making the snow white pillars gleam. Ahead, at the end of wide hall, were two sets of double doors, with round golden handles hanging down limply. The doors to the left were the ones he seeked.
Pushing one of them open, he found the people inside as they were the last time he was here, gathered around a circular, wooden table. Three men and a woman, wearing different uniforms, looked up as he entered. There were only five seats at the table. Four were taken, so Archer took his place at the fifth.
Turning the screen of the monitor at the center of the table to face him, he logged in. He was asked to give his time period and ship name and class, and he chose his name from an alphabetical list of hundreds of Starfleet captains.
"Archer, Jonathon." The computer confirmed.
Archer leaned back in his chair and glanced at each of the people in turn. To his left, was Captain James T. Kirk, dressed in a gold shirt and black pants that just touched the tops of black boots. Archer knew he would command the USS Enterprise NCC-1701 in about a hundred year's time. Beside Kirk, sat the bald-headed Jean-Luc Picard, also Captain of a ship called Enterprise. His uniform shirt was red with black over the shoulders, with little rank pips shinning in the chandelier light. To Picard's left was the dark-skinned, and also bald, Benjamin Sisko. His uniform was black, with grey at the shoulders, and red showing at the neck. He was Captain on a Cardassian space station that Starfleet had taken over. To the left of Sisko, and to the right of Archer, sat Kathryn Janeway, her short brown hair framing her face. Her uniform was black with red areas at the shoulder. She was the Captain of a ship that had been stranded in the Delta Quadrant, which Archer knew was a long, long way away from Earth. Of course, the little room in the large embassy was a long way away from Earth, as well. He didn't know where, exactly, just that it was farther than any human had ever been. In his time period, anyway.
A person materialized in the room suddenly. He looked human, though Archer, and the other Captains, knew very well he was not. The alien spoke English perfectly and clearly, though they knew it was not his mother tongue.
"As you know, Captains, you are here to learn about a threat. I have more information, and a plan of action against the threat."
"What kind of threat are we dealing with?" Kirk asked. "Stellar phenomenon? Alien threat? Who exactly is being threatened?"
The alien leaned over between Sisko and Janeway and put five padds on the table, one for each Captain, each getting the padd that's used in their own time frame. Archer read his, knowing it contained information and details on the unknown threat.
"An alien species from the Andromeda Galaxy, as you call it, will conquer the galaxy, and threaten to take over other galaxies with the new power and technology they will acquire from your galaxy."
Archer read through the padd, listening to the alien talk and the other Captains question him. He said nothing, only observed and read from his padd. The aliens in question called themselves the Xenonians. Why a race would name themselves that, Archer didn't know, but wanted to. He read on, discovering that they'll come to the Milky Way through a wormhole in the center of the galaxy.
"Excuse me." Archer interrupted the Alien. "What do you mean that the aliens will come into the galaxy through a worm hole at the center?"
"In the center of your galaxy–"
"Our galaxy." Archer interrupted. "Meaning you're not from around here?"
"That is talk for later, Captain Archer. At the center of your galaxy, there are two black holes, as you know. Both are dormant during your time period, but will become active within two hundred years."
Janeway barely stifled a gasp.
"One of them is not a black hole, as it seems. One is a wormhole, connecting your galaxy to the Andromeda galaxy. It is through this wormhole that the Xenonians will invade the galaxy."
"Why will they do it, Ambassador?" Picard asked. "What will happen that will influence them to come here?"
The Ambassador moved over toward the window, light from an unknown source streaming in and bathing his face in golden warmth. "If acid were to rain down from the sky, what would happen?" He reached out the window, feeling for something unseen by the Starfleet Captains. There was a soft snap, and the Ambassador came back to the table with a pink-white flower in his hand, more beautiful than any flower that Archer had ever seen. "Life would die. The acid kills it. Nothing could survive under such a harsh, choking rain."
"What are you saying?" Sisko asked, thoroughly confused.
"Even with a black hole at the center of your galaxy, the wormhole remains, sucking up all the remains spewed out by the black hole. The wormhole exists within the black hole, and the black hole within the wormhole."
"So you're saying they're right on top of each other." Janeway simplified.
The alien Ambassador nodded.
"That still doesn't explain why the Xenonians will attack." Kirk said impatiently.
"A black hole sucks up everything near it, as you know." The Ambassador explained. "Since the black hole and wormhole are within each other, everything that goes into the black hole goes through the wormhole, where it is dumped out the other side. In this case, the Andromeda galaxy. Comparing this to my earlier analogy, the waste from the black hole is the acid rain."
The Captains were silent for a moment, thinking over what the Ambassador had just told them.
"If there's a black hole on top of the wormhole," Archer asked finally. "Then how will the Xenonians get from there to here without being destroyed in the process?"
"They will harness the power of the black hole, use it and the power of the wormhole as a sling shot or catapult. They will use its tight pull to their benefit."
Archer shook his head in disbelief, his motion shadowed by the other Captains.
"Enough has been said." The Ambassador said. "You must return to your ships to think on what you have been told. Your next visit will be four days from now, and I will tell you the plans we have made to protect your galaxy and the Andromeda galaxy."
"Wait." Janeway said. "Who are you?"
The Ambassador hesitated a moment, but that moment was so brief, Archer wondered if he had imagined it. "I am a Guardian. That is all I will say… for now. Be gone, now!"
The white dream-like haze that surrounded everything brightened to an unbearable ivory glow. Archer could see nothing but whiteness, until it died down and there was nothing but darkness.