Halka looked much the same in this universe as it did in mine. The Enterprise had arrived here and achieved orbital insertion two hours ago. We were currently moving into the same position relative to the planet and its star as last time. This was supposed to maximise our chances of forging a link between the two universes once more. That was the theory, at any rate. I wasn't convinced this was going to work, but there was no way I was going to miss it. Which is why I was on the bridge when the test commenced.

"We are ready to proceed, Captain," said Mr Spock, frowning over his instruments, "though I must caution you again that the power required for this exercise will leave the Enterprise without shields and phasers while the device is active."

"Duly noted, Mr Spock, but we're just going to have to chance it. Any sign of hostiles nearby, Mr Sulu?"

"Negative, Captain," replied the helmsman, "we appear to be the only vessel present for several light years in every direction."

"Then proceed, Mr Spock."

Spock depressed a button on his console and our deflector dish began emitting a high energy beam of exotic particles focussed on an area of space a kilometre or so in front of the Enterprise. We followed the action on the viewscreen as the beam shot forth, watching for something to happen.

And then it did.

A disk started to form, a circle of space outlined by a glowing rim. It grew rapidly until it was larger than the ship, forming a window into another universe. And on the other side of that window, facing us, was another starship projecting an identical beam from its own deflector dish. The disk had formed at the interface where the twin beams met. We recognized the other ship immediately.

It was the Enterprise.

I frowned. Had my Spock taken possession of a similar device in our universe and been ordered to Halka to test it? But no, this wasn't my Enterprise - the markings were wrong. Which meant it wasn't my universe on the other side of that portal, either.

"We're being hailed, Captain," said Uhura.

"Onscreen, Lieutenant."

An image appeared of the bridge of that other Enterprise, but it might just as well have been a mirror. There was no analog of me, but they were all there, Kirk, Spock, Uhura, Chekov, Sulu, all dressed in regulation Federation uniforms.

"Greetings, Captain," said the other Kirk, "and may I say that's a fine looking crew you have there."

"I believe I can say the same of your crew, Captain," chuckled our Kirk.

"This is an historic moment, the first contact between our two universes. I'd very much like to meet in person. May we send over a party."

"A private word, Captain?" said Spock.

"You'll have to excuse me, Captain," said our Kirk, "I'll get back to you shortly."

"Of course," other Kirk replied, as Sulu broke the connection.

"What is it, Mr Spock?"

"I tried scanning the other vessel but could not. They are blocking all scans. Additionally, while you were communicating with their captain, I analysed the image we were receiving from their bridge and believe it is being altered as it is transmitted."

"So they're hiding something?"

"That would appear to be the case, yes."

"Keptin," said Chekov, "the other ship has just beamed down a landing party to the capital city of our Halka."

The portal between our universes was large enough that each of us could see some of the other's Halka through it. That had been enough for them to beam a landing party through as the Halkan capital city came into view.

"Size of the landing party, Mr Chekov?"

"Twenty people, all apparently unarmed."

"Twenty? That means their transporter has more pads than ours."

"There's something else," said Chekov.

"What is it?"

"They're registering as human, but not entirely so."

"'Not entirely so'? What does that mean?"

"I'm sorry, Keptin, I don't know how else to describe it."

"Uhura, re-open communications."

"Aye, Captain."

The bridge of the other Enterprise appeared on the viewscreen once more, complete with its smiling crew. There was something unnerving about the way they all smiled at us, even their Spock. It seemed almost...predatory.

"Why have you beamed a landing party down to our Halka?" asked Kirk.

"We are explorers, Captain, our Prime Directive compels us to seek out new worlds, new civilisations, and to boldly go where no human has gone before."

"A fine sentiment, and one we share, but the diplomatic protocols of first contact require us to begin by establishing agreed procedures before this sort of incursion takes place."

"'Incursion'?" said other Kirk. "You make it sound like some sort of prelude to invasion. We beamed down twenty specialists, none of them armed, as I'm sure your scans will confirm. We would be perfectly happy for you to beam a similar team down to our Halka. Please feel free to do so."

"Thank you, but we'll hold off for now. Clearly, we have opposing approaches to first contact. These are the kinds of cultural differences that can lead to real problems if we don't explore them first and resolve any areas of possible conflict."

"I see your point and appreciate your concern. Perhaps we could meet on your ship to discuss these matters?"

They seemed awfully eager to get aboard our Enterprise. Too eager.

"Keptin," said Chekov, "twenty people just beamed up to their ship from the planet."

"So their landing party has returned?"

"No, these were not the same people."

"Why do you have Halkans beaming up to your ship?" our Kirk demanded of his counterpart. "Did they come of their own free will?"

"Of course, Captain, what do you take us for? The Halkan Council sent up a delegation to greet us."

That didn't sound like the Council, that didn't sound like them at all. The Captain agreed.

"So quickly?"

"We can be very persuasive."

"Keptin," said Chekov, interrupting. "Those strange readings I got from the twenty who beamed down..."

"Yes?"

"I'm now getting them from forty, no fifty..."

"What is going on?" said Kirk, leaping to his feet.

"Teams from the other ship have beamed into transporter bay and deflector control," said Sulu. "We've been boarded, Captain."

"Cut the beam from the deflector dish, NOW!"

Chekov's fingers raced over his console, to no avail.

"I..I can't, Keptin! We're locked out!"

I had redshirts stationed in deflector control. I took out my communicator and flipped it open.

"Radic? Michaels? Come in please."

Silence.

I tried the transporter room.

"This is transporter chief Williams," said a voice over the sound of phaser fire, "they're over-riding our lock-out and pouring through and...no!"

He screamed, and the line went dead.

"What are you doing?" demanded the Captain, shouting at his counterpart.

"I should have thought that was obvious. It's the interaction of the beams from our two deflector dishes that creates the portal and is keeping it open. We knew you'd turn yours off as soon as you realised we were a threat, collapsing the portal, and we couldn't have that. While we could beam down to the planet, something about the exotic particles we're both emitting to form the portal, some sort of interference, was preventing ship-to-ship transport. We kept you talking until we could figure out how to compensate for this, which we have."

"Captain, I believe I am now able to penetrate the false image they are projecting and display what lies beneath."

"No need, Mr Spock," said the other Kirk. "The time for subterfuge is over, so let me save you the effort."

The image changed. For the first time we saw the other bridge as it really was.

"Bozhe moi!" swore Chekov, while Uhura gasped, her hand flying to her mouth.

The rest of us were shocked into silence by the sight, and by the sudden realisation of just how much trouble we were in.