Things weren't going Supergirl's way.
The day had begun as an attempt to stop a rampaging giant Metallo from wrecking Metropolis had turned into a near death losing fight.
If only Superman were here, rather than off saving some distant planet with the Justice League.
She never had a chance. Metallo saw her coming from a mile away and shot her down with kryptonite laced energy blasts. If only she had been more experienced in fighting supervillains, Supergirl could have used super-hearing to anticipate Metallo approach.
Oh well. Supergirl could always try and attack from afar. She flew in from a different direction and shot some heat vision at him from behind, but it didn't seem to affect the mechanic monstrosity at all. Metallo seems to have gotten an upgrade.
After getting thrown backwards yet again, Supergirl landed right into the STAR labs building. As she struggled to get up, Supergirl observed that she was in a room with what seemed to be some sort of portal nearby. She vaguely remembered a Daily Planet story on inter-dimensional experimentation by the facility.
Supergirl saw a small vial of yellow fluid that seemed to glow with unnatural energy on the floor. Her microscopic vision revealed a form of energy not altogether dissimilar from the solar energy that fuels the powers of all Kryptonians. But there is something else, something more… ethereal…
Supergirl immediately felt the desire to consume the vial's contents. Although she had misgivings about swallowing the unstable substance, curiosity quickly got the better of her. Besides, maybe this STAR-made substance could help her defeat that upgraded overgrown bucket of bolts outside.
As soon as she swallowed the liquid, Supergirl began to glow as her uniform changed into a black and yellow uniform with a glowing white "S" appearing against a black background. As Supergirl leapt into the air, she did not notice that her eyes were glowing white or that she was flying at a much faster speed than usual.
When Metallo perceived Supergirl returning to face him, he shot another bolt of kryptonite-laced energy at her, only to find that it had no effect on her. Supergirl responded by shooting one energy bolt from her hand. When it hit Metallo, he disintegrated into thin air.
Once Supergirl descended to the ground, she could hear the cheers of the citizens of Metropolis. The city was grateful for its salvation from the menace of the metal behemoth. A large portion of the city had been damaged by Metallo's rampage, but most of the reconstruction could be done in a matter of months, if not weeks.
Of greater concern to Supergirl as she flew off to the Watchtower to wait for the return of the Justice League was the nature of the serum she consumed. What did it do to her? Why did she feel like she was being supercharged by a dozen suns? What powers did it grant her? And why was she hearing dark, sinister sounding voices in her head?