Read the below fic with "Victor's Piano Solo" from Corpse Bride in mind.
"I see you."
Chell immediately ducked behind an open panel, resisting the urge to squeeze her eyes shut. Always keep your eyes open, even if there are bullets flying at you. Bullet holes peppered the wall next to her, nearly grazing her arm. She pulled the portal gun off of her hand and experimentally rotated her wrist. Possibly the worst thing she could do right now would be not taking proper care of herself and losing strength in her arm in the middle of a test. Such as right now.
She allowed herself a silent sigh and was about to peer around the corner at the turret when something caught her eye behind the panel she was currently using as a shield. Like many of the Rat's dens, the panel was propped open by a weighted cube, but Chell could have sworn that for a moment she saw the disappearing corner of a white lab coat. She edged around the metal bar and crawled across rusty grates through a dim tunnel-maybe this time she would actually see the Rat. Maybe he could lead her out himself this time instead of going through and painting black arrows. But even as she crawled forward she realized that she was being silly. There had been no sign that the Rat had been here recently. And why would he know the way out of all of Wheatley's new test chambers?
Chell paused at the end of the tunnel. It had led into a large white room that looked suspiciously like a test chamber, although there were no cameras. Her tired eyes darted around, trying to figure out if any of the panels would suddenly slide open to reveal a turret. She shot a blue portal up near the ceiling in case she needed to dispose of something quickly.
"Uh, hello?" a male voice echoed from somewhere far away. Chell winced. "Where, where did you go? I still need you to test, you know, although it's, ah, yeah, I know that was a difficult one. But seriously, I can't see you anywhere."
Chell rolled her eyes and finally allowed herself to step down out of the tunnel, positioning her gun so she could fire at any moment. When she stepped onto the faded white flooring, it rumbled a little and Chell quickly withdrew her foot, looking around wildly and backing out of sight. A panel opened in the center of the floor, and up rose a black… machine? It had what seemed to be a low bench in front of it. The rumbling stopped, and Chell stepped out again, cautiously walking forward to inspect the… instrument. That's what it was. A piano.
"Wait, did you hear that?" Wheatley's voice sounded a little closer, and Chell automatically glanced back at the tunnel. "Oh yeah that was the sound of you. Failing that test. Because, uh, suddenly leaving the testing area is grounds for immediate failure. But you can still come back!" he added quickly. He started rambling on, growing increasingly more annoyed, but Chell was only half-listening.
The piano seemed almost to glow, shiny and black against the stark whiteness of the wall panels. Taking one last hawk-like glance about the room, Chell sat down on the bench. The keys were so stark, ebony and ivory. If not for her bright orange jumpsuit it might have been that all the color in the world had been drained way. Chell cautiously let go of the handle of her portal gun and set it on her lap, on hand so that it could be drawn at a moment's notice. The button on top still glowed blue, reminding her of the recently shot portal.
She took a cautious breath pressed a key. The middle C. The note rang out strong, and Wheatley suddenly stopped his chattering. Chell pressed the E a third above the C, then the G, making a perfect major chord. The piano was miraculously in tune.
"Were you not listening to me?" Wheatley said angrily, "I said, come back here this instant and continue testing! And what the heck was that?" His tone changed. "Was that… a piano?"
"Obviously, moron," Glados muttered, and Chell started a little and looked down at the potato affixed to the end of her gun. GlaDOS had been quiet for a few tests after an unsuccessful attempt at giving Chell a tip. Chell worried that the A.I. had been fried, but the only thing to do had been to keep testing.
The notes of the chord finally faded away, and Chell ran her fingertips over the tops of the keys, frowning in puzzlement. Her fingers itched to play something, and her fingers slowly found the correct notes-a few high ones played by her right hand, and then she carefully placed her left hand down in the lower octaves. The song came so easily, just like testing. She closed her tired eyes. It did feel a little like testing, honestly, except that there were no bullets, no bruises, and no A.I.s yelling at her. There was just the rush. The song built, and she opened her eyes again to watch her own hands pound, clawlike, at the keys. She thought she could hear Wheatley saying something in the distance, but she ignored it. She felt new, raw, almost happy. It was like the music had replaced water. It revitalized her, and she realized she was smiling away, smiling and maybe crying-when suddenly the piano jolted. The panel underneath it started falling away, and Chell grabbed her Portal gun and leapt out of the way. The last disjointed chord rang in her ears eerily, but she didn't take time to watch the piano fall. She looked to the top of the chamber, and saw that Wheatley had opened up a panel to poke his little robot body in. She glared, and her eyes darted around, searching for an escape route.
"Found you!" Wheatley said, and started, once again, to go off on a tangent, but Chell wasn't listening. She shot a portal at the panel above Wheatley, then at her feet, so that she landed on his back, and started, once again, her mad dash across Aperture.
She would escape. And with music back in her life, she had that much more reason to escape alive.