The military came up the ruined avenue with rifles raised, and for one bad second Sam thought the whole thing would unravel right there.
Lennox was at the front, helmet gone, face streaked with concrete dust. He saw Megatron standing free and uncuffed beside Optimus, and his weapon came up, and forty other weapons came up behind him like a wave.
"Stand down," Optimus said.
"That's Megatron," Lennox shouted. "That is the thing we just lost half a city to."
"Captain." Sam stepped into the gap, which was, he would think later, the single stupidest thing he had ever done, and he had once tried to buy a Camaro with no money. He held up both empty hands. "It's over. The Cube's gone. He's. He's not the same."
"Kid, get out of the line of fire."
"No." Sam planted his sneakers in the rubble. Behind him he could feel Mikaela move up to stand at his shoulder, and that steadied him more than anything else could have. "You want to shoot him, you go through me. I just spent everything I had putting something back in him. I'm not going to watch you blow a hole in it."
There was a silence then that had weight to it, the kind of silence that decides things.
Megatron broke it. Slowly, with a grinding of servos that had not been built to do anything humble, he lowered himself to one knee. The fusion cannon folded back along his arm and stayed dark.
"I will not raise my hand to your kind again today," Megatron said. The words came out of him like teeth pulled. "Take that, human, for the small worthless thing it is."
Lennox stared. "Did the giant murder-robot just surrender?"
"I think," Mikaela said, "he just promised. Which from him is probably bigger."
Lennox did not lower his rifle. But he did not fire it either, and after a moment he keyed his radio and told command, in a voice that suggested he expected to be relieved of duty for it, that the situation was contained and to hold all air strikes.
That was when the sky changed color.
It started as a stain in the thinning smoke, a bruise of orange that did not belong to any fire on the ground. The clouds began to turn, slow and deliberate, the way water turns when something is rising through it. Every Cybertronian in the city went rigid at once, Ironhide and Ratchet and the limping wreck of Jazz, all of them snapping their heads upward like animals scenting a storm.
Megatron rose to his full height. The old cruelty came back into his frame all at once, but it was pointed somewhere else now.
"He felt it," Megatron said. "The instant I changed, he felt it. Across the whole of creation, he felt his slave slip the leash."
A single point of light tore open in the clouds, and through it, unfolding like a thing too large for the sky to hold, came the Fallen.
He did not land so much as arrive, a column of black and burning gold settling onto the husk of a parking structure that crumpled beneath him to powder. Ancient. Wrong. His optics were not red or blue but the dead white of a star that has already collapsed and only looks alive because the light has not finished traveling.
"MEGATRON," the Fallen said, and the word cracked windows for a mile. "WHERE IS MY ALL SPARK."
Megatron stepped forward, and Optimus stepped up beside him, and the sight of the two of them shoulder to shoulder seemed to genuinely confuse the ancient thing, the way a man might be confused to see his own right hand shaking the left.
"It is spent," Megatron said. "Spilled into the world. There is no weapon here for you, master. There is nothing here you can use."
"YOU," the Fallen breathed. "YOU LET A FLESHLING UNMAKE A MILLION YEARS OF WORK."
"He let me remember," Megatron said, "what you spent a million years making me forget."
The Fallen raised one hand. Sam saw it happen in slow motion, the air around that hand starting to glow, the pavement beginning to lift in flakes as gravity itself thought better of the spot. He understood, with the same wordless certainty the Cube had given him, that whatever was about to leave that hand would not leave a Mission City behind it.
And Sam, who had no Cube, no weapon, no plan, did the only thing left to him. He looked at the empty cavity in his own chest where the All Spark had passed through, and he reached for it anyway.
It answered.
Not all of it. Most of it was gone, poured out into Megatron and into the world. But the Cube had used him as a needle, and a needle keeps a little of the thread. A thin bright filament of it had snagged in Sam Witwicky and stayed, and when he reached, it came up burning in his palm, no bigger than a coin.
He did not have enough to heal the Fallen. He could feel that. The thing in front of him was too old, too hollowed out, a spark that had chosen its emptiness so long ago that there was nothing left in it to give back to.
But he had enough for one true thing.
"Optimus," Sam said. "You said the matrix. The Leadership thing. When it's gone you can't make it. Right?"
Optimus turned his great battered head. "Sam. What are you doing."
"Making one," Sam said, and threw the coin of light.
It struck Optimus square in the chest, over the gaping wound the Fallen had not even needed to make, and Sam watched the last of the All Spark do the only thing it had ever truly wanted to do. It gave. The light sank into Optimus and bloomed, and where there had been a dying engine of a heart there was now something that blazed like the core of a sun, the Matrix of Leadership reborn out of mercy instead of war.
Optimus straightened. His wounds closed over with new metal. And when he raised his arm the energy that gathered there was not a weapon of the war but the clean white fire of creation turned, for once, against the thing that had perverted it.
"You taught us that the strong rule," Optimus told the Fallen. "You were wrong. The strong protect."
He and Megatron fired together.
The Fallen did not scream. He simply came apart, the way a lie comes apart when the truth finally arrives, and the bruised sky overhead snapped shut and went, at last, ordinary gray.
In the ringing quiet afterward, Sam sat down hard on the asphalt because his legs had stopped agreeing to hold him.
Mikaela dropped beside him and pressed her forehead to his temple and said nothing, which was perfect.
Megatron looked at the place where his master had been for a long time. Then he looked down at Sam, and there was no leash in his optics anymore, and no hate either, only the vast tiredness of someone setting down a thing he had carried so long he had forgotten it had weight.
"Four million years," Megatron said, "and it ends with a boy who would not let go of a box."
"In my defense," Sam said, "I'm really stubborn."
Optimus offered his brother a hand, the new light still burning behind his chest. After everything, Megatron took it.
And above the broken, smoking, saved city of men, the sun came through.