As we all know, Man of Steel could be the beginning of a Justice League line of films. However, in order to get to the Justice League, a few things need to be established. We need a new Batman film to establish that this isn't Noland's Batman. Two, we need to re-establish Green Lantern after the horrendous Ryan Reynolds film bombed. Three, We need to introduce Wonder Woman. Four, we need to decide which Justice League group to use in the film.
How can we manage all of this in a reasonable amount of time? It's simple, skip a World's Finest movie and just go straight into Trinity. Trinity can begin in the same way as a World's Finest film. For some reason, Batman makes his way to Metropolis and encounters Superman. Superman immediately thinks that the Gotham City vigilante is trying to cause trouble in his city and battles him. The two spend the first half hour of the film squaring off against each other, but soon come to develop a mutual respect and realization the neither can defeat the other. Batman reveals to Superman that he came to Metropolis to get the Man of Steel's help. Wayne Enterprises satellites encountered an extra terrestrial armada moving toward Earth.
The two then discover that Lex Luthor has located the lost island of Themiscira and Atlantis. He plans to send a team of highly trained soldiers to both locations in order to increase his financial empire to have a nation all his own. Superman and Batman get to Themiscira several hours after Luthor's soldiers to find them already battling the island's inhabitants lead by Princess Diana. The Amazons battle ferociously as Supes and Bats join the battle on their side and defeat the soldiers. But Queen Hypolita isn't thankful to the two, instead chooses to place them into custody for breaching the boarders of her island and plans to execute them for the actions of the soldiers, because to her all men are equally dangerous and have no place on her island.
Diana chooses to stand up to her mother and tries to talk sense into her. Hypolita isn't moved and declares that the two will be killed at dawn. Diana sneaks into the Amazon's prison and helps the two escape, but before they can leave the island the queen and her army of Amazons are waiting for them at the shore line. Realizing that the men had allowed themselves to be imprisoned and could have escaped at any time, she grants their release but because Diana had betrayed her sisters and her Queen she was instructed to leave with them and never return. The three leave the island and head for Superman's Fortress of Solitude where they discover that Luthor's forces had attacked Atlantis after they left Themiscira and that Atlantis had seen this attack as a declaration of war by the surface world. Diana reveals that she knows the Atlantian king and at one time they were to marry in order to unite the two lost kingdoms of Greece, but eventually realized they were not meant to be lovers. Diana takes the Dark Knight and Man of Steel to meet with Arthur in order to try and make him realize this was an isolated attack and was not a declaration of war.
The King agrees to speak with them but isn't moved to call off the war. By Atlantean law, if they want the king to do something but he refuses they must each battle him one on one. If all three lose, the war would continue and all three would be executed. But if even one of them manages to succeed, the war would be called off and the three would be free to go. Because of the depth of Atlantis, Superman doesn't receive quite as much solar energy so he's not 100%, and Batman is weakened do to the amount of pressure being placed on his body. The King of Atlantis manages to defeat them both but they put up a great fight and earn his respect. Finally, Diana is forced to battle her one time lover in an epic battle which ends in a stalemate. Because of this, the king orders his army to stand down and releases the three. Before they leave, Aquaman tells them that they've earned his respect and admiration and declares them allies of Atlantis. The film ends with the Trinity back at the Fortress of Solitude keeping an eye on the alien armada as it nears Earth's solar system.
The next film would be a Green Lantern reboot. But how does DC get around doing the same old Hal Jordan origin story that's been done over and over in film and animation? It's simple, pull a Hulk! A reboot sequel would be perfect. During the opening credits do some kind of a flash sequence that shows Hal's origin as Green Lantern and include Sinestro putting on the yellow ring. After the opening sequence, we see Sinestro being disciplined by the Guardians for trading his Green power ring for a yellow and reveal that they had discovered his treatment of his home world. At this point, Sinestro reveals his true intentions and destroys the Guardians' chamber just before he escapes, which makes him enemy #1.
Shortly after this, Carol Ferris is abducted by a bright pink light which is revealed to be from an alien race who are closely related to the Guardians. They chose her as their queen and transform her into the Star Sapphire. Wile on Earth, Hal Jordan is forced to train a new lantern recruit as his partner, ie Guy Gardener. All communication with Oa, the other lanterns and the Guardians is down due to Sinestro's attack so Hal and Guy are caught completely unaware when Sinestro begins his attack on the two. During the battle, Star Sapphire senses the catastrophic battle taking place on her home world between Fear and Will and decides to take matters into her own hands by traveling to Earth in an attempt to stop the destruction. When she gets there, she sees Guy Gardener unconscious and Hal exhausted and bloody at the hands of Sinestro. Because of her love for Hal, her ring takes control over her and sends her into a psychotic rage against Sinestro. Hal attempts to help her, but she fires a blast from her ring that sends Jordan flying through the air just as Guy awakens. Because of this, Gardener thinks she's a friend of Sinestro's and attacks her. While Guy and Carol are keeping each other busy, Sinestro continues his attack on Jordan.
Carol manages to get the better of the rookie Guy, and proceeds to once again attack Sinestro. Hal attempts to get Carol to let him handle Sinestro, but Carol backlashes against Hal and attacks him. Carol, Hal and Sinestro begin a 3 way battle of rings as Guy once again attempts to join in on the battle by attacking Sinestro, while Hal and Carol battle each other. Eventually, Hal manages to get Carol to over ride her ring's control and the three quickly join forces and defeat Sinestro.
As Carol returns to Zamaron, Hal and Guy return Sinestro to OA to face trial. Once Sinestro is sentenced for his crimes, The Guardians announce that Guy will receive full Green Lantern status for his part in defeating Sinestro and that the two will return to Earth as the first of the thousands of sectors to be policed by 2 Green Lanterns. On their way back to Earth, they notice a fleet of alien battleships making their way into Earth's solar system. At the moment they realize an invasion of Earth is eminent, they quickly rush home. In a post credits scene we receive glimpse inside the lead ship of the alien armada where a robed druid like figure is kneeling in front of a thrown speaking to a dark figure cloaked by shadows with glowing red eyes.
The third film would introduce The Flash, by revealing his origins and have him facing off against Captain Cold and Boomerang. The film ends with the Rogues being arrested by the Flash and what appears to be an eclipse over the entire planet. In the post credits scene, Green Lantern (Hal Jordan) introduces himself to Barry Allen and informs him that he needs the Flash's help to save the world.
Now we have Justice League! The film opens with the sound of pounding... As the camera moves into focus, we see Superman working his way through a government facility. He makes his way to a highly protected room in the center of the facility, several hundred feet below ground. Just before the scene ends and the opening credits roll, we see Superman enter the protected room where a large green alien is being held. End Scene, cut to opening credits. After the opening credits, a fleet of alien battleships have entered Earth's Solar System and are moving closer and closer to Earth. Inside the lead ship, we see a druid like figure kneeling before a thrown which an enormous dark figure sits, the only this visible are his hands, feet and glowing red eyes. The figure soon stands up and reveals himself to be Darkseid, the God like ruler of the planet apokolipse. It's revealed, Darkseid was drawn to Earth because his scientists received intel from his Kryptonian soldiers who said the Last Son of Krypton was on Earth. After Zod and his soldiers never returned from Earth, Darkseid assumed that Kal-El had defeated his General and prepared for an invasion, hoping to capture the Last Son of Krypton and make him his new military general and enslave Earth. He gives the order to send his ground forces through the Boom Tubes and begin the invasion.
Portals begin opening all over Metropolis as alien forces begin attacking the city of Krypton's soul survivor. Darkseid takes over all of Earth's media sources and demands their immediate surrender as well as the location of the Kryptonian they call Superman. While the forces of apokolipse begin their invasion, Green Lantern (Hal) and the Flash make their way to Metropolis and battle the armada, while Batman and Wonder Woman join them with some assistance from Aquaman. Immediately after Darkseid's broadcast, Superman returns to Metropolis with the Martian Manhunter and confronts him. As soon as Superman shows himself, the invaders stop their destruction almost as if being controlled like robots. Just then, a Boom Tube opens to reveal Darkseid standing face to face with the Man of Steel. The two share in some small talk as Darkseid tells Superman he and his adopted planet will surrender one way or another. He offers the Man of Steel 1 hour to decide, before he sends his "Demons" back to begin the invasion again. At this point, The group of heroes fall back. The group then engage in battle with the forces of Apokolipse once more until finally, Darkseid decides to take on the Last Son of Krypton himself. The two engage in a disastrous battle while the other heroes continue their war against the "Demons". Finally, Superman manages to unleash the full force of his powers on Darkseid forcing him to declare defeat as he's taken back to his ship to return to Apokolipse. The group of heroes are celebrated by the entire world after their victory and the media dubs them the Justice League.
At the end of the film, it shows the League converting one of Wayne Enterprises satellites into their "Watchtower". Aquaman returns to Atlantis telling the others that if they need his help again he'll be there. Green Lantern decides to fly to Zamaron to see Carol, giving the League his ring's frequency so they can contact him if needed. Batman quickly disappears leaving only a note that reads if needed again call, attached to a button which activates an alarm in the Batcave. Martian Manhunter agrees to stay on the Watchtower and monitor things. Just before the credits roll, we see Superman Flying from the Watchtower and heading toward Earth in true Reeves fashion. In a post credits scene, we see the Flash looking out one of the windows saying to Martian Manhunter "Great, how am I suppose to get home?" end movie.