This would function as basically Green Lantern Corps 1.5/Justice League Interplanetary 1.5, in the same way that Captain America: Civil War was Avengers 2.5 (this sentence will be utter gibberish in a handful of decades). We open on an attempt to fortify Oa against Jordan’s oncoming assault, with John Stewart told this defense is their only hope of stopping Jordan. To safeguard their power supply, the Guardians send Kyle, Jade and Soranik Natu (I’m going to keep pushing this love triangle, because done right it’s good, clean character drama), because, “There is another.”
The basic idea is that Jordan wages war on Oa, taking on most of the heroes from Green Lantern Corps., and decimating most of the unnamed ranks yet again. Jordan is also doing something different this time around- he’s taking rings and/or absorbing power from the defeated Lanterns on both sides. He attacks the Guardians, and absorbs as much of their power as he can before John and the gang show up and give him some actual resistance, at which point he flees- absorbing the energy he can from the central battery.
Soranik Natu interrogates Sinestro, for information on Jordan. At first he’s too proud, and refuses to admit to his errors (reversing some of his growth at the end of the last movie, not because he can’t change, but because real change is rarely a flicked switch). She softens, and asks him to tell her about her mother. Sinestro tells her that when he first became a Lantern, he tried to save Korugar from a military junta. However, upon overthrowing the junta, the planet looked to Sinestro for leadership. At first, he hardly weighed in, his intention having been to free his people, not rule them. On one of his periodic visits, however, he caught the eye of Katma Tui, a passionate activist who wanted him to use his influence to make Korugar into the planet it could be, rather than the planet it was. The pair fell in love, and she encouraged him to put in place reforms to make the planet more democratic, and kinder to its lesser citizens. Over time, however, their love faded, and his duties to the Corps meant that he neglected both his love and his world, and in his name his hand-picked administrators created a dictatorship crueler than the junta it replaced, using green energy weapons to signify Sinestro’s power, and leading the people to hate Green Lanterns. When he finally returned, he found that Katma Tui had fallen out of love with him, and had given birth to their daughter. As one last show of love for her and their people, she asked that he put things right, and dismantle his government- quietly. Sinestro did so, orchestrating the overthrow to look like a popular revolution. However, his abuse of power was discovered by the Guardians. They stripped him of control of his home Sector and rank within the Corps.. To keep Katma Tui quiet about these indiscretions, they inducted her into the Corps. and gave her control of the Sector. However, Korugar still mistrusted the Lanterns, especially Sinestro, who they called ‘the Wicked’, and held Katma Tui as suspect, calling her ‘the Lost.’ While Tui vowed to use her power to protect her people and those like her across the Sector, she recognized that to give her people peace of mind she would have to do so from the shadows, while her sister raised Soranik in her stead.
Soranik asks where her mother is now. Sinestro admits that she was not among those he fought on Oa, and that she hasn’t been seen for some time. He tells her there are rumors she is one of the Shadow Lanterns, lanterns given the dual mandate of maintaining the quarantine around sector 0666 (I imagine they read this as, ‘Zero-triple-six’ just because reading it out loud as , ‘Sector Six-Six-Six’ feels a little too silly); he’s never seen her, or any other Lanterns, there, but given that he was violating the quarantine, was doing what he could to avoid those guarding the Sector. Soranik tries to transition back to the interrogation without hardening her manner, but he resists, until she calls him, “Dad.” Sinestro relates that Jordan called him a fool, that he mocked him for thinking he could prevent the Blackest Night, that he saw his sniveling fear as readily as a child’s. He told Sinestro there was no breaking the black wave- that the only rational thing was to cleave to their loved ones and mourn the dark death racing towards them- but that at least Hal could try to put right was Sinestro broke- that Sinestro believes Hal means to resurrect Coast City.
Hal proceeds to Earth. The human Lanterns arrive first, because they’re willing to spend energy to move faster- time is of the essence for them, while Jordan requires every last drop for what he’s about to do. They speed to Earth, and contact Justice League Interplanetary, who rally the Earth’s defenses and heroes to try and stop Hal. See, there’s a problem with Hal’s plan- the Lanterns really can’t create life; the closest such attempt by another, earlier Lantern, to undo his failure to save a planet from destruction, raised an army of half-alive monstrosities that nearly razed the entire sector. There’s also the very real possibility that in combining the green and yellow energies, he’ll create a release of energy that could cleave the planet in half. “So if he fails, everybody dies. If he succeeds, everybody dies,” John Stewart sums up. The heroes assemble messily. It might pay to have the major teams have an ‘assembling’ montage, so we see the Justice Society discussing the threat, and the League, and the Interplanetary League, Outsiders, Outlaws, Birds of Prey, etc.. We get a big, bombastic series of montages and action pieces, as the Batman-related characters try to defend Gotham, the Superman-related defend Metropolis, etc., all a feint to draw attention from Jordan’s real target, where Justice League Interplanetary and Stewart and the other human Green Lanterns are waiting, because they know what he plans to do.
Unfortunately, they can’t stop Hal. I imagine we get quite a few little fights between Green and Yellow Lanterns, until Hal descends. He takes on both Superman and Martian Manhunter at the same time, frantic that they’re spending energies he needs to try and resurrect Coast City’s fallen, lashing out at them more violently for it. I imagine he eventually just flattens everyone, friend and foe alike, taking all the rings and basically using his rings to make energy hands to operate the additional rings. At that point, Jordan knocks Superman out of the galaxy; we see a red and blue blur go flying out of the system and beyond. At the same time, he seals Manhunter in a bubble, squeezing the volume of air. Hal explains that the Lanterns have extensive files on Martians, and that increasing the pressure in the bubble will increase the temperature, until the Manhunter’s flesh reaches its firing point. Manhunter screams, instinctively turning intangible and falling from the sky in a ball of fire, which is, mercifully, extinguished on impact with the soil.
Jordan turns to the task of recreating Coast City. We watch it build up, a brick at a time, at first. We see Jordan’s eyes, as he processes all known information from government and internet sources about every citizen of Coast City, lingering when he reaches Carol, and he whispers, “Carol,” as his voice catches. The other Lanterns are helpless to resist, still ringless. Superman returns, and Stewart fills him in on what he missed, and asks if Superman can stop him. He tells him he can’t- not without killing those people. Superman points to the light constructs, and tells Stewart that they are, down to the atomic level, alive, that he’s in the process of reconstructing them on the molecular level, that it would be the equivalent of taking a million people off of ventilators at the same time. The light coming off the rising city dims for a moment, and we cut back to Hal, who grimaces, and begins to shake because he needs more power. A yellow light shoots from Jordan towards the sun, and we see a fireball sucked along it, as the city returns
Superman is troubled, but recognizes that he can’t let billions die to save millions. Stewart stops him, and tells him there might yet be another way. I imagine we won’t show much of what Kyle, Jade and Soranik Natu’s mission entails, because it’s kind of a reveal, but they could have a skirmish with some Yellow Lantern stragglers that’s going poorly, until there’s a purplish light, and we cut away, but here’s where it pays off:
Carol Ferris floats to Jordan, flying over the light construct of Coast City he’s trying to will back into existence. She tries to engage him, but he assumes she’s just another ghost haunting him. “I’ve had enough of ghosts!” a distraught Hal yells at her, refusing to stop… until she strokes his cheek, and he stops, and whispers her name, and asks “How?” his voice breaking.
She tells him she wasn’t in Coast City… but her heart aches for those who were. He asks again, clarifying- how is she there now, how is she flying? She uses her powers to peel away her civilian clothes, revealing her (probably less revealing than the one in the books) Star Sapphire costume. “What, did you think you were the only one who got to go on interstellar missions for remote alien civilizations?” she asks with a light laugh.
He maybe tells her that statistically he would have assumed so, yeah. She flies to his side, this time directing his eyes to the sky, and the sun, and what his yellow ring was doing to power his reconstruction. “What-“ he’s taken aback by what he’s done, the damage he’s done to the entire planet. Hal’s going to heel-face turn, here, and work with the heroes to fix the sun.
This is an excuse to gather all of the bigger brains of the DC Universe into one room. They’re somewhat at a loss, because none of this should be possible, and no solution should be workable. Hal insists there is one, that he has more computing power at this fingertips than they have on the entire planet- even if they were networked in a way to leverage it- which they aren’t, that if he can at least get the sun back to a degree of homeostasis, knocking it off the unstable path its on, now, that should work- it might not put all the years back on the sun’s dial, but stop it from prematurely going nova.
It’s totally possible to keep Hal alive after this part, but I have plans for him, you see, very black plans indeed… so I’d have Hal sacrifice himself to save the Earth. I think you could get a really poignant moment out of it, Carol and Hal flying towards the dying Sun to reignite it, her determined to do whatever it takes to save him, him determined to do whatever it takes to make up for what he’s done. But eventually she fails; her powers aren’t enough to protect the both of them from the heat and gravity, and she stops him for their tearful goodbye. She tells him love should conquer all; that if he comes back with her they can figure out another way, together. He tells her the damage he did to the sun is so severe, it will be irreversible by the time they could make it back to the planet. “I can’t be a man who deserves you if I don’t make this right. I’m sorry. You truly deserved better than me.” He flies into the sun, and a moment later, there’s a ripple of green and yellow energy that reignites the Sun- but its beaten to Carol by green energy pushing her far enough back to be unharmed by the it- Hal’s last gesture is saving the woman he loves as a Green Lantern.
Superman and Ion salvage the green lantern rings from the sun, leaving the yellow ones there. The depowered Yellow Lanterns are taken into Waller’s custody. Clark hands over John’s ring, and Stewart tells him they should talk, about the prophecy of the Blackest Night.
Credits. Mid-Credits scene: We see a red-skinned Green Lantern flying on the edge of Sector 0666 (I’d probably have some familiar-looking planets from the beginning of Green Lantern Corps.); she looks a bit like Soranik Natu. She’s flying in a relatively straight line before veering suddenly, narrowly avoiding a blast of red energy. I’m currently undecided; in the books, Atrocitus used the blood of the other four Inversions to power his battery. It might save time/amp up the threat if the other Inversions become Red Lanterns themselves; an unkillable hierarchy of ring-powered terrorists rightfully pissed about the massacre of their homeworlds… that sounds pretty terrifying. And of course they recruit the cat, because a pissed off cat Lantern sounds like fun. Tui manages to evade the Inversions, hiding in an asteroid field. The Inversions start smashing their way through it, flinging kilometers of rock away at a swipe. Atrocitus tells them to leave her, he wants the Oans to know they’re coming, because there isn’t a thing they can do to staunch the Rage of the Red Lanterns. Dex-Starr, a cat with a Red Lantern ring on its tail, attacks Tui in her hiding place, clawing at her face, before being torn clear by one of the other Red Lanterns, and scampering off after them; Dex-Starr doesn’t float, at first, but bounds from red energy ledge to another to gather up speed before flying. Tui sends out an all points bulletin: there’s another Corps. of Lanterns, and they’re headed straight for Oa.