Mirror, Mirror, On the wall

The Hromi Cluster. Close to the Klingon border, Starfleet ships are routinely assigned to patrol the cluster and ensure that there are no Klingon raiding parties present. One such ship is the U.S.S. Aurora, a modified Stargazer Heavy cruiser, retrofitted for tactical duty. The captain of this ship, Kurt Boyson, is currently in his ready room, overlooking a report regarding the main deflector.
“Bridge to Boyson.” The comm chirps. Boyson lowers the PADD to his table.
“Go ahead.”
“Captain, there is an unidentified anomaly 3.2 light years off the port bow.”
“Change course to intercept. I’ll be right out.”
Boyson picks up his jacket and heads out onto the bridge. His First Officer, Commander Casey, steps out of the command chair and takes a seat in her chair. Boyson sits down and places his foot on his knee.
“Lieutenant Lawson, give me a science report. Ensign, change course, bring us within 500,000km of the anomaly.”
The Aurora banked left and proceeded to the anomaly. (According to a later report, the anomaly appeared to an inverse Antiproton collapse in subspace.)
“Captain, the sensors aren’t calibrated enough to get a detailed reading, but I can-“
The ship starts moving toward the epicentre, shaking violently as the engines attempt to hold position.
“Helm, report!”
“Captain, we’re being pulled in! The impulse engines can’t stop it!”
“Full about! Warp 6!”
The Aurora turned 180 degrees and attempted to jump to warp, at the same time as the nacelles entered the anomaly.
U.S.S. Marie Curie.
“Captain, the Aurora has entered the anomaly. Sensors have lost her.”
“Understood Lieutenant. Now we wait.” Replied Captain Kellick.
“Sir, the Aurora has returned.”
“Open a channel.”
“Aye sir. Channel open.”
“Captain Boyson, what can you report?”
U.S.S. Aurora
“Sir, incoming hail from the…U.S.S. Marie Curie.”
“U.S.S.? I thought she had a Vulcan registry, being a D’Kyr Class.”
“Captain, she’s a Luna Class.”
“What? Open a channel.”
“Captain Boyson, what can you report?”
“Captain? Where’s Commander Mallory?”
“Commander Mallory has been dead for 6 weeks. You were there at the funeral.”
Captain Boyson makes a motion to cut the channel. Turning to his bridge staff, he asks for any ideas.
“Captain, it’s possible that this is a Klingon or Undine trap. Recommend we raise shields.”
“Negative. Until I know for certain, that is a Federation Starship.”
“Sir. The anomaly. We went to warp as we passed through. It’s possible that we warped into a parallel reality.”
“Hmmm. I’ll take your word on that Lieutenant. Open the channel.”
“Captain, without going into details, something has happened. I am not your Boyson.”
“An alternate Boyson? Intriguing. Regardless, we should leave the area. The Klingon fleet will be returning shortly. Set course 310 Mk 42. Engage at warp 9.”
“Understood Captain.”
The Aurora and the Marie Curie jumped to warp, just missing a Vo’Quv Class Klingon Carrier drop out of warp…

Outpost Argo
The Aurora and the Marie Curie dropped out of warp at the station, and Captain Boyson was shocked at the sight.
“Captain...there’s over 50 refugee ships at the outpost! Along with the Aurora and the Marie Curie, there’s only the Luna and the Yamato here!”
“Calm yourself. We will find out.”
Suddenly, there was a transmission over the fleet channel.
“Commodore Greywarden, please meet myself and Captain Boyson on the Ops floor. We will need to talk.”
Outpost Argo – Ops Floor
Captain Boyson and Captain Kellick arrived on the transporter pad and stepped into the Ops Floor. Boyson came face to face with Commodore Greywarden and two security guards.
“Jesus Gideon. What happened to you?”
“Commodore, apparently, this Captain Boyson comes from a parallel universe.”
“Easy way to confirm that.” Greywarden turned to a security officer.
“Run a quantum scan on the Captain.”
The security officer pulls out a tricorder and scans Boyson.
“Commodore, his quantum signature is different to ours. This is not our Captain.”
The Commodore pauses, and lifts his hand to his chin.
“Well Captain. Looks like you’re telling the truth. This is a good thing. We can use you-“
“Commodore, with all due respect, I have to get home.”
“Captain, we could use your ship! From the scans, at the moment, she is the most heavily armed ship docked here.”
“But what about the Yamato?”
“The Yamato has no weapons, Captain. Her phaser lance is currently on the station, her torpedo launchers are mounted to mines guarding the approaches, her phaser arrays are mounted on the exterior station.”
“I see…Commodore, my apologies but I have to return home.”
“Captain…I’m sorry but I can’t allow that. Escort the Captain to his quarters. Treat him with respect, he is still a Captain.”

3 days later
“Captain, we’ve been going through this for three days. We need you-“
The station’s computer suddenly sounded.
“Dammit. All hands to battlestations! Scramble all ships!”
“Commodore…this isn’t my universe, but get me back on my ship, and I’ll do what I can.”
“Thank you Captain.”
The Commodore and the Captain ran to the transporter pad, the Commodore heading to the Luna and the Captain heading to the Aurora.

U.S.S. Aurora
“Captain on the bridge!”
“At ease. Prepare the ship for launch. Red Alert. Incoming hostile contacts.”
The Aurora eased out of her berth and began to engage the incoming Klingon ships. While the Aurora has a full complement of weapons, the constant barrage starts to buckle the shields, several disruptor bolts strike the hull.
“Emergency Evasive Riker-1!”
“Negative Captain! The Bussard Ejectors are offline!”
“Dammit! Target the Bortas’qu! Fire everything!”
“Captain, I’m picking up more ships.”
Several Cardassian and Romulan battleships, led by a Hermes Class ship, drop out of warp and begin attack the Klingon’s from behind.
After several hours the Klingon’s are routed.
“Captain, incoming communication from the Glaive.”
“On screen.”
“Kurt, I leave for a day, and you bring Klingon’s to the base. I’m insulted.”
“Paxal? You have not called me that in 3 years.”
“Paxal. I am not from this universe.”
“Captain, incoming communication from the Luna.”
“Captain, can you see why we need you?”
“Yes Commodore.”
Captain Boyson turned to his bridge crew, and receiving nods from them all, turned to his helm officer.
“Ensign, set course for the Hromi Cluster. Maximum warp.”
The Aurora jumped to warp, the Luna following.
“Captain, we are being pursued by the Luna.”
“Understood. Prepare the tricobalt device.”
Hromi Cluster. Sector 476-A
The Aurora dropped out warp and immediately came about. The Luna dropped out 30 seconds later.
“Open a channel to the Luna.”
“Channel open sir.”
“Commodore, your ship cannot stop me. Do not make me remove one of the few combat-capable vessels left to Starfleet.”
“Kurt, please! I need the Aurora to help my people!”
“Commodore, I cannot help. This situation is covered by the Prime Directive. I cannot do more than I already have.”
Captain Boyson turned to tactical.
“Lieutenant Commander, fire.”
The tricobalt device launched from tube 3, and detonated about 600km away from the two ships.
“Boyson, you’re a pain in my ass…you know that?”
“Yes Commodore.”
Commodore Greywarden watched as the Aurora warped into the subspace tear.
“Commodore, I’m picking up another ship. It’s…the Aurora! Our Aurora!”
“Open a Channel!”
“Commodore, it’s good to see you again.”

Prime Universe.
“Gideon! Cease fire! Escort the Aurora back to base. I’ll tell you everything…”
<c>" Chief Rex to Argo. Prisoner escape! Security breach! Need intercept!"

<c> "The Azorious copies chief. releasi'n docking clamps... moving ta intercept" replied Gideon

no sooner had The Azorious cleared her moorings then they saw the Aurora go to warp..

"Pursue em lieutenant.... maximum warp..." As Gideon entered the bridge and sat in his newly acquired command chair.

The Azorious' newly refitted engines surged as it plunged through space pursuing the rogue vessel.

" 'soon as they drop out, hail em 'n go ta red alert" Ordered Gideon.

Soon after, the Aurora dropped out of warp near a subspace tear and began to position itself to pass through. Seconds later the shape of the Azorious loomed over it, dwarfing the escaped ship.

<c> "Kurt, what the hell do ya think yer doin'? Drop yer shields n prepare to be beamed aboard. No ones got ta get hurt today."

<c> "I'm sorry Gideon, I have to do this. I have to get home."

<c> "Kurt ya got no idea if this 's even gonna work. Yer putt'n all yer crew lives at stake 'ere on ah hunch. Ya willin ta throw their lives away too?"

<c> "Don't you understand? They are stranded too! My entire crew! This is not where we belong Gideon. We have to go home."

<c> "Ya may be 'ere instead o where ya think ya need ta be, but 'least yer all alive man..... don't make me do this.... ah can't let ya..."

<c> "Gideon... we are going home and you aren't going to stop us."

<c> "Ya can't hold up to this ships firepower Kurt. Ah'm sorry but this 's gotta end"

"Cut the comm... power to weapons. Target his shields n weapons, do not destroy em..jus get em where we c'n get em back ta Argo" Said Gideon.

"Captain! something is happening! Im detecting some kind of energy surge from the Aurora" exclaimed the tactical officer.

"Shit.... evasive!... come about and prepare ta fire.... on my mark... ready................................ what the hell? where is he!!"

"Sir its seems he has somehow disabled our short range sensors with that energy burst... attempting to find him visually" replied the leiutenant.

"Damnit find him!..... There! there he is!... I dont know how he turned so fast but lock on to his shields and weapons generators!"

"Hail incoming captain... it's the Aurora"

"Get those shields down.... put it on screen..."

<c> "Gideon! cease fire! Escort the Aurora back to base...I'll explain everything..........."