The Cost Of Power.

Summary: AU story. When Optimus tells Sam to push the AllSpark into his chest, what if Sam did it didn't kill optimus?? What if it gave him the power to defeat Megatron, but exacted an unforseen cost?

Rating: M

Warnings: crack, gender-bending, AU, violence.

Disclaimer: Transformer's ain't mine. It belongs to Hasbro and Paramount/Dreamworks.

A/N: thanks to Sanja of the Nerdene Hyrde for sparking this bunny.

The Cost Of Power

Chapter One: An Act Of Last Resort.

Sam scrambled backwards as Megatron, wounded by the Air Force, but still determined, dragged himself towards him.

"I'll kill you!" threatened the silver mech. "Mine! All Spark!" Sam scuttled back from the enraged silver giant.

"Sam, push the Cube into my chest! Now!" Optimus cried to Sam. Sam hesitated but didn't have time to think, and whirling, he did as Optimus had asked.

Optimus staggered as Sam fled behind him, the Cube flaring like magnesium from where it had stuck between Optimus' chest plates. Optimus looked in pain, Sam saw, and suddenly he recalled what Optimus had said about 'sacrificing himself'. A lump rose in Sam's throat and his belly felt as if it had frozen solid: had he just slain the Autobot leader and his friend? Was Megatron weakened enough by the Air Force's attacks for the rest of the Autobots to destroy?

Once again, Optimus staggered as Megatron howled in rage, but then Sam noticed Optimus become more steady. Optimus himself seemed to be glowing, radiating a golden light, just as the AllSpark itself was doing. The light brightened, until Optimus' own frame wasn't visible any more, rather there was an Optimus-shaped pillar of brightness. The brightness moved, seizing hold of Megatron. Megatron struggled, howling, trying to shoot at and flail at the eye-searing form ahead of him.

The attacks did nothing to the shining Optimus-light, but then the huge mech cried out and froze as the brightness spiderwebbed over his body, and Sam and the rest of the Autobots watched in stunned silence as the hole in Megatron's chest sealed up, the leg that had been blown off was regenerated, and all the battle damage was healed. Megatron's cries died abruptly, and the bright figure caught Megatron and knelt to lie him gently on the ground as the light in his optics dimmed.

At that point Mikaela drove up in the pickup with Bumblebee. Bumblebee gave a whistle of surprise when he saw the bright form, but then shuttered his optics and warbled, an odd, beautiful music. The bright Optimus-light sang back, similar but different, unearthly and beautiful. For a few seconds the two sang, the music of the two songs mingling and playing a counterpoint around each other. Then the singing stopped.

"The AllSpark…has healed Megatron, but the Cube itself has been destroyed." Bumblebee said sadly. "Its physical form has been obliterated." Bumblebee paused to let everybody absorb this statement.

The AllSpark was the source of almost all life on Cybertron, the source of the Sparks of all those standing before him. Unless at least one femme managed to reach them - and was willing to bear Sparklings for them - their race was in danger of extinction. Bumblebee continued speaking before discussion of this issue took over from the rest of the message the AllSpark had given Bumblebee.

"It understood that it was a move of last resort, but said that there will be a cost, though I do not know what that cost will be. It says Megatron will recharge for a while, when he onlines again, he will not be a threat any more…" Bumblebee tailed off as the glowing form approached him and crouched, seizing hold of Bumblebee, who gave a startled squawk but then went quiet. As they watched, the light that still obscured Optimus' form spread to cover Bumblebee, and when it drew back from the scout, they saw that the energy had regenerated the legs that had been blown off by Starscream at the beginning of the Mission City battle.

Sam blew out a breath of air. All this dire talk of a cost had made Sam wonder if the AllSpark would take Bumblebee's life as payment for the power Optimus had wielded, but no, instead the AllSpark had healed his scout friend. He was glad, he hated to think that it might heal Megatron but destroy Bumblebee. It seemed wrong somehow. Though that still left open the question: what was the cost? Again Sam tried to swallow a lump in his throat as he figured that maybe using the power would mean the death of the mech who wielded it.

As if to confirm his fears, the bright form slowly crumpled. Sam want to rush forward but Ratchet held him back.

"No, Sam, the energy level is high and currently highly chaotic. We do not know what effect it may have on a human."

"But - Optimus Prime!" Sam cried.

"Whatever has happened has happened, Sam, the energy is dying back. It should be safe enough to approach shortly, but whatever is happening, there is nothing anyone can do to stop it." Ratchet told him. As he finished speaking, as if to prove his point, the light faded and died, leaving a crumpled heap where it had been. Optimus looked subtly different in some way, though Sam could not say how.

He was about to pull himself free from Ratchet when Optimus groaned. Sam sighed in relief: it seemed that Optimus was alive.

"Optimus?" Ratchet asked. "Prime! Are you well?"

"Dizzy..but well." Optimus confirmed , then got to his feet.

Everyone stared as Optimus stood and unshuttered his optics. His paintwork was gleaming, the battle damage gone as if it never had been, but that was not the only difference, and even Sam could see what had happened. It seemed the AllSpark had exacted some sort of price from him after all.

"Why are you all staring at me? Is there something wrong?" intoned the 28-foot tall blue and red flame-patterned femme.