This entry covers the entire “First Contact” crossover, including the issues:
Worlds’ Finest Annual 1
Batman/Superman issue 8
Worlds’ Finest issue 20
Batman/Superman issue 9 and
Worlds’ Finest issues 21 – 22, in that order.
Worlds’ Finest written by Paul Levitz, Batman/Superman written by Greg Pak
Wildstorm Concepts:

First Contact is the story of the first meeting between Huntress and Power Girl, natives from Earth-2, with Superman and Batman from Earth-1. In their Earth, the girls were the daughters of their Superman and Batman, so this meeting is especially significant for them. Most importantly, perhaps, the whole story involves Gamorra!
It starts off with a prelude showing the past of Earth-2. It is dedicated with the youth of Huntress and Power Girl, who called themselves Robin and Supergirl when they lived in their Earth.
One night the World Government was holding a big summit of nations, so Supergirl thought it was a great opportunity to go out and party. She meets a really cute guy in a bar: Ken Gammora. Yes, Gammora with two M’s. It seems it is spelled like that on this Earth. They hit it up, get some chemistry going on between them and end up kissing. Ken admits he has to leave the following day, though. He’s the son of the leader of Gammora, and they’re going home after the Worldgov conference is over. Supergirl is so touched by the confession that she actually considers revealing her secret identity, but suddenly there’s an explosion in the Worldgov tower. A terrorist attack! While Ken runs to check if his dad is okay, Supergirl suits up and starts playing hero. Clearing off rubble, putting the damage back together, moving fast enough not to be seen clearly. But she isn’t fast enough for Ken.
When he went back to see if Supergirl was where he left her, the room crumbles over him, and Ken is killed. Supergirl is heartbroken. The rest of the issue is dedicated to the search of the person responsible for the explosion; a warrior from Apokolips. But that isn’t relevant for us.
The story continues years later, in Earth-1. The Apokolips warriors from before ended up destroying Earth-2, so Robin and Supergirl had to run to Earth-1. Now they call themselves Huntress and Power Girl. Lately Power Girl has been losing control of her powers, so they go to Superman and Batman to ask for help. Batman calculates Power Girl’s powers are fluctuating towards a city called… New Gammora! (Actually, sometimes it’s written like Gamorra, but I’m pretty sure it’s supposed to be Gammora with two M’s.)
Originally the place was Rheelasia, a crime infested dump run by drug dealers and gun smugglers… until a couple of years ago when someone named Kaizen Gammora took over, turning the place into one of the fastest-growing economies in the world. But wasn’t Kaizen turned into Regulus in the pages of “Team 7”?! I can think of two explanations for this. 1) After being beaten by the Birds of Prey, Kaizen and Higgins split apart and Kaizen regained his youth. 2) This isn’t Gamorra, but Gammora. Two different people; no relation. None of these explanations is very satisfactory. If Gammora is some new player, why did he name his city “New” Gammora?
Anyway, this is what happened: After Huntress and Power Girl escaped from Earth-2, Apokolips and its legions defeated the rest of the heroes quickly enough. Their brainwashed all of the heroes, turning them evil. But even if that Earth’s Superman had become a soldier for Apokolips, he still missed his daughter. He managed to create a portal to Earth-1, where he made contact with Kaizen and convinced him to help him capture Power Girl. He gifted Kaizen his advanced technology, nanite constructs, which allowed Gammora to grow incredibly fast as a country. Kaizen just had to release his nanites into the air; if they touched a kryptonian he would be able to steal information and energy from them. Soon enough, Power Girl was touched and this is what caused her to lose control of her powers. Using her DNA, Kaizen started creating an army of clones for his army. This is when Batman and Superman step in.
After being told they must go to New Gammora, the girls recognize Kaizen as “Ken”, the guy Power Girl dated back in Earth-2. The group decides to pay the city a visit to investigate. They go under disguises, but their covers get blown fast. At first Kaizen welcomed Power Girl, acting like her powers went out of control inadvertently because of a test his people were running, like it was all a misunderstanding. Kaizen says he just wants to help Power Girl return to her home Earth. At the same time, though, Batman discovers Kaizen has been grafting the kryptonian DNA codes his nanites have been stealing onto humans; building an inhuman army. And it seems the nanites affect any kryptonian, not just Power Girl, so Superman is affected too. And Superman losing control of his powers equals massive destruction. To contain him, they’re left with no choice but to put a kryptonite collar around him.
While Batman and Power Girl battle the army of Gammora, Superman and Huntress have to deal with just having destroyed an entire street. Superman is either powerless with the kryptonite or uncontrollable; he calls his ally Toyman, asking for an emergency delivery of a containment suit. Luckily, Toyman had a prototype ready from an off-planet theme park he was developing a few years back. Superman puts it on so he’s able to repel the nanites. Meanwhile, Kaizen begins using his nanites in the opposite way; draining Power Girl of power. He uses the energy to fuel a portal to Earth-2, opening a gateway for his masters from Apokolips.
At first, opening the gateway lets a huge amount of energy into the room, so powerful it burns out all the nanites. Problem is, not even Superman was powerful enough to do that. As it turns out, the energy comes from Apokolips, and the girls are shocked to see their home planet has been overrun by forces of evil. In fact, they refuse to accept the portal is working right; that can’t be their Earth.
Kaizen is covered by Apokolips’ energy, which gives him powers and strength. He uses all his might to try to throw Power Girl into the portal, but in the end she manages to throw him in instead. While the quartet of heroes takes a breath and discusses if the girls should go through the portal or not, Kaizen comes back. He’s been turned into a giant, made even more powerful by the Superman of Earth-2. Kaizen brings a couple of Parademons, Apokolips’ soldiers, with him. The heroes manage to defeat the bad guys, but Earth-2 Superman speaks to them from the portal, seducing Power Girl to go to him. When she recognizes he’s actually her dad, she agrees to go – but right when she’s about to, Huntress destroys the portal. She just wasn’t convinced that it was their Earth.
While the girls argue, Kaizen ends up in Earth-2. Due to having failed him, Superman condemns him to a lifetime of torture. Anyhow, with its government destroyed, New Gammora is sure to fall into chaos. Superman and Batman decide the most heroic course of action is to get the hell out of there.
The last issue is little more than an epilogue. While the girls lie in the ruins of New Gammora, arguing with each other, they get interrupted by forces of A.R.G.U.S. Apparently the organisation wants to take New Gammora’s technology. That’s not wrong on its own, but they confuse the girls with Gammorans and start attacking them – even bringing in a tank. Power Girl is super powerful, so the girls are just happy to receive these goons to release their tension on. After that, they fly back to the United States. How very bland.
Next: StormWatch Vol.3 issue 0, written by Peter Milligan.