The Doctor bounced into the TARDIS with his new ever-cheery spirit and began setting controls on the console. He didn't even notice Rose until she gave a melancholy sigh.
"What is it?" he asked plopping down in the seat next to her. "What's that?"
She touched the gadget on her lap gently. "Oh, just something of Jack's…one of his little techy things."
"You miss him, don't you," he said quietly.
"Did he die, Doctor?" she asked, lifting her head; now he could see her red eyes and wet cheeks. "Did Jack die there?"
Her lip trembled and she bit it, fighting back her tears. Impulsively the Doctor gathered her into his arms, rubbing her back and soothing her.
"Did he die?" she asked again.
"No, Rose, he didn't die," he said quietly.
"What?" Rose sat up, disbelief written on her face.
"He didn't die." The Doctor got up and went back to the console. "Jack is alive and…well." He listened impassively to Rose expressing her joy. "Alive, but at what cost?" he muttered to himself.
A calm settled over the TARDIS, quiet and peaceful. Then Rose said,
"Hey Doctor?"
"Yes Rose?"
"Knock-knock."
He turned and saw a familiar grin. He almost sighed. "Rose, I still don't understand this game of yours."
"Oh c'mon, just do it! Knock-knock."
"Who's there?"
"Doctor."
"Doctor who?"