The Doctor turned away from the one who broke the promise with Clara in his arms. He started to walk forward, not knowing where he was going, just knowing he had to leave.
"Clara. We will get out of here. I promise you. I won't lose you again. We will survive this, Clara," the Doctor mumbled as he trudged forward.
His foot caught on a rock and he stumbled. He clutched Clara to his chest as he fell to his knees. Clara whimpered slightly. He could feel his time stream sapping away his strength the longer he was there.
"Almost there, Clara. We're almost there. Just hold on," the Doctor said.
He stood up and looked around. He couldn't see a way out. He started walking forward again. He walked for minutes that felt like days. He stopped and fell to his knees in despair. He hung his head and hugged Clara, if it were possible, even closer to his chest.
"I'm sorry, Clara. I'm so, so sorry," the Doctor whispered into her hair.
Clara mumbled indistinguishably. The Doctor leaned his ear next to her mouth so he could hear.
"What did you say?" he asked.
"...and remember," she whispered.
He looked down at her in confusion. Suddenly, an explosion of faces went off in his head. A bright light burst into being only a distance off at the same time. He looked up, then smiled down at Clara.
"You clever girl," he whispered down at her. He kissed her forehead. "I remember."
He stood up and looked at the light. He took one shuffling footstep forward and then another. For each footstep, he thought of another companion or person he had met on his travels.
Sarah. One step. Sarah Jane. One step. Leela. One step. Amy and Rory. Two steps. Rose. One step. Ace. One step. River. One step. Mickey and Jackie. Two steps. Martha. One step. Tegan. One step. Jo. One step. Jamie and Zoe. Two steps. Craig. One step. Strax. One step. Wilfred and Donna. Two steps. Ian. One step. Jenny. One step. Harriet. One step. Vastra and Jenny. Two steps. Astrid and so many others.
He took a few more steps and then stumbled and fell only one step away from his way out. He looked at the pillar of light in despair. The time stream had taken away all of his strength. He didn't think he could take that one step.
"Remember me."
The Doctor looked down at Clara as those two words echoed as if she had shouted them, but she lay as motionless as before. He brought his hand up and held her face.
"My Clara. My beautiful, wonderful, impossible Clara. How could I possibly forget you? The girl who has saved me twice and thousands of other times and died doing it. The girl who stole my hearts. The girl I've lost so many times. How could I forget you?" he asked quietly.
He looked up at the pillar with fire in his eyes.
"I can't and I will not lose you again, I promise you," the Doctor growled. With a grunt, he hoisted himself up onto his feet, cradling Clara carefully to his chest once more.
"Let's be cleverly impossible together, eh," he said with a smile as he stepped into the pillar and out of his time stream.