The Doomsday Machine
The Mirror Kirk, stood at he main control panel in the Constellations battle bridge. Through the static on the view screen, he could see the maw of the planet killer as it slowly drew the ship in. He pressed a button on the panel, a thirty second countdown began.
Kirk picked up his communicator, "Kirk to Enterprise, beam me aboard."
On the Enterprise bridge, the bearded Spock was sharing a kiss with Yeoman Janice Rand. He turned to the intercom and said, "Umm, no."
"Spock, you miserable traitor, beam me aboard, now. That's an order."
"Captain," Spock said, "logically, you should have known this day would come. But, don't worry, for your "suicide" run against Commodore Decker's planet killer. I will recommend you for the highest award the Empire offers. Perhaps you may even get a bust in the Hall of Heroes, next to Empress Hosi Sato."
The countdown continued. 4...3...
Kirk screamed, "Spooooooock."
The Constellation exploded and the Doomsday Machine drifted dead in space.
Spock stood up and said, "Now that I'm Captain, my first...". He froze and his face contorted in pain. He looked at Rand.
"What did you do to me?"
She licked her fingers seductively smiled and said, "Oh, poison. Harmless to humans, but kills Vulcans in seconds."
Spock reached for her throat and collapsed at her feet.
Captain Janice Rand stepped over the Vulcan's body and took her rightful place in the command chair. She picked up the Yeoman's data pad.
"Chekhov.". She snarled and threw it at him. "You are the ship's new Yeoman."
He jumped up and yelled, "Nyet.". Then drew a phaser. Sulu, Uhura, and Scotty all sprang up and drew their phasers. The door to the turbo lift opened and Dr. McCoy burst into the bridge. A phaser rifle in each hand. All at once they screamed,. " I'm the Captain now.". And opened fire.
It's not clear what happened next, but the best guess is that in the ensuing fire fight, someone's phaser beam struck a power conduit triggering a chain reaction that reached to the engineering section.
A warp core breach destroyed the Enterprise instantly.