"DIB!" roared Zim, not sure if he had heard himself right the first time.

"Yes, it's me, Zim!" snapped Dib, as unpleased to see Zim as the Irken had been to see him. He looked a bit older than Zim had remembered, with some gray hairs at the temples and some wrinkles on his cheeks, but there was no mistaking the Dib for anyone else that Zim had encountered in all his travels, especially not those Planet Express monkeys.

Seeing Dib's enormous head again, though, was the last straw for the Irken invader. First he had had to deal with those delivery service fools for a solid week, and then he had found out that the Almighty Tallest had completely forgotten about him and his mission on Earth, and now he had discovered that his greatest enemy of all had survived into the 30th century!

"How did YOU make it all this time, silly earth monkey?" roared Zim again, his clenched fists extended far above his head.

"My father was a brilliant inventor, Zim, and figuring out a way to cheat death was only one of his many accomplishments," replied Dib proudly, while still scowling down at his old enemy.

"After he was placed into cryogenic suspension because of a rare illness, I took over the family business and made 'Membrane' a household name. I made a host of pertinent discoveries in the fields of both scientific research and paranormal study and … hey, why I am telling you all this?"

"Silence!" cried Zim, just as enraged as he had been all those centuries ago when he had matched wits with Dib on a daily basis. Well, maybe not matched, as Zim felt Irken intelligence to be infinitely superior to human thinking; but parrying with Dib day in and day out had infuriated Zim back then, and now all that old fury had flared up again a millennium later.

"Don't you order me around, I'm a thousand years old!" retorted Dib. "I have to admit though, Zim, that after you up and disappeared in the 21st Century, I was at a loss for what to do. When I finally convinced myself that you were truly gone for good, I was able to concentrate on the really important things in life. I earned scientific degrees from Cal Tech and MIT and went on to actually make something of myself, instead of just wasting all my time trying to foil your ludicrous plans of conquest."

Dib smiled mockingly, his tone colored with disdain.

"So in a way, Zim, I guess I have you to thank for all this!"

Zim looked at Dib as if he had never seen him before.

"So you want to thank me for you being a head in a jar?" chided Zim.

"Hey, everybody does this nowadays!" shot back Dib incredulously. "Only the best of the best get their heads preserved, and I've been voted one of the greatest people to ever live!"

Zim crossed his arms across his chest and stared at Dib, his green lower lip twitching with anger, his one violet eye larger than the other. He thought back to those halcyon days of time on Earth when he had planned to win a skool election, and subsequently have Dib's head removed and filled with salted nuts … Then Dib started talking again and shook Zim back to the present/future.

"So thanks again, Zim," expressed Dib. "Without you having left, I might still be wasting my time trying to stop an Irken invasion that was never going to come!"

Dib practically spit out the last few words, bubbles rising in his jar but quickly dissipating at the surface.

Zim stood steadfast, as if accepting a challenge.

"Guess again, head boy!" shouted Zim, shaking his fist at Dib and sounding as if he were preparing to play a hidden trump card.

"I'm going to get back to that long-ago time and bring the Massive to Earth! The Irken armada will finally overrun your pathetic planet, and then you'll be lucky to be a huge head in a giant toilet tank! Ah-ha-ha-ha-ha!"

"How are you gonna get back, Zim?" queried Dib, one eyebrow set higher than the other.

Zim was taken a bit aback by the question. Truth be told, he had no idea how to accomplish the task, and had hoped that someone here in the future would have told him by now.

"I'll get back," he snapped, shaking his fist again. "I'll fly the Voot Cruiser right back to the point where I left, and then you will pay – oh, how you will pay!"

"Good luck with that, Zim," mocked Dib. "From what I remember, your little space ship has nowhere near the power needed to traverse the space-time barrier, so unless you build yourself a time machine, I guess you're stuck here in 3000 with the rest of us! Ha ha!"

"Well ..." started Zim, looking around and twiddling his thumbs, obviously flustered. "Perhaps ... someone with ... great intellect could ... build one?"

The words hurt as they came out, and sounded as if Zim were begging, which wasn't too far from the truth.

"Yeah, right!" chortled Dib, pleased with seeing his old enemy sinking so low. "Like I'd ever help you get back!"

"Yeah, well – your head is huge!" replied Zim, at a loss to say anything else. He was pleased to find that the words still stung Dib after all these centuries, though.

"My head is not big!" cried Dib, shaking in his jar and spilling some fluid over the top.

"Yeah, well, not from where I sit," said the standing Zim. "But then, only someone with a huge head could possibly wield the intellect to build a time machine."

"You're not gonna catch me with that trick, Zim!" shouted Dib. "You'd have a better chance of getting caught in an explosion to propel you back in time and … ahhhh!"

"That's it!" yelled the wily Zim. "All I have to do is generate an explosion, and I'll be sent back to Earth in the past!"

"Me, too?" queried Gir, looking up from where he had been sipping fluid from Yanni's jar.

"Yes, Gir, you too," said Zim matter-of-factly.

"Guess again, Zim!" bellowed Dib. "You'd need an explosion equivalent to the strike of a bolt of lightning to do that, and ... why do I keep doing this?"

"Well, it's true," said actor Christopher Lloyd from another shelf in the room, the thespian having performed such a feat cinematically in the "Back to the Future" trilogy.

"Lightning it shall be then!" howled Zim, pointing up menacingly at Dib, when there was a commotion around the bend and he heard several futuristic voices he recognized, voices belonging to the Fry, Leela and Professor humans, plus that giant frog woman Zim had just met.

"They're here!" hissed Zim, sensing his time was short. "Gir, hide! Quickly!"

"Okey-dokey!" squealed the droid as he began to careen about the hall, looking for a safe place to disappear. Dib, though, was only too happy to help out his old acquaintances.

"HERE!" he cried at the top of his head. "They're in here!"

"Oh, you horrible, interfering Dib!" shrieked Zim, as several pairs of footsteps came closer …

TBC