'Should have sonic'ed that,' the Doctor thought as he heard the roof door bang once, then twice behind him. He focused on the device in his hands. All he needed to do was destroy this relay. That was all. Didn't much matter if he made it out or not. Not like he had anything to live for…not anymore. He flinched slightly as he heard the whine of Auton weaponry.
Surprisingly, there was no pain, just a soft exclamation, then a warm weight pushing into his back. He twisted about and aimed his sonic screwdriver at the Auton, disabling it.
The Doctor sighed as he looked down at his savior. He was, for reasons unknown, relieved beyond measure that it wasn't the blonde girl - Rose, wasn't it? - that he'd met earlier that evening. But still, this one was young. Far to young to have given up her single, precious human life for the likes of him. He carefully brushed long, dark hair away from her face. The Doctor felt a strange ripple in the timelines as he saw her face. Pretty, pixie-like features were bathed in sweat and twisted in pain, but impossibly, her eyes fluttered open and focused on him.
"Doctor…"
"Who are you?" he asked, bluntly.
"A friend."
"Not bloody likely," he muttered, but his hands were very gentle as he lifted her into his lap. Whoever this girl was, she shouldn't die alone. He had that much common decency left in him. "Stupid little ape," he whispered brokenly. "Why'd you do it?"
"It's what I do, Doctor. I save you, so you can save the world." Despite her obvious pain, she seemed content in this knowledge.
"But why? I'm not worth it. Not worth anyone else's life. How old are you? Twenty? Twenty two? Not worth it," he said again, with finality.
"But you are. You are worth it." One small hand curled around the edge of his leather jacket, and there was a hint of steel in her voice when she spoke again. "You make it worth my while. Leave enough time on that explosive and get yourself out of here. Promise me."
The Doctor stared into her beautiful brown eyes and felt those strange ripples in time again, and an odd compulsion to obey her. "All right," he promised.
The girl shivered in his arms, and he knew that she was fading fast.
"And Doctor? That girl you met earlier? Find her."
He nodded.
She pushed at him weakly with her hands. "Run…run you clever boy…" She sighed softly and was gone.
The Doctor held her close for a moment, then kissed her forehead and laid her gently down on the roof. He didn't even know her name. He considered her still form, then reset the timer on the explosive. Five minutes ought to be enough. He turned and ran.