"Where are you off to?" the Doctor asked, not bothering to turn away from whatever fascinating tinkering he was doing with the TARDIS console.

"I was going to take the train into London," Clara replied, a touch evasively. "You promise not to leave without me, right?"

"Cross my hearts," he replied. "We're here for twenty four hours while the TARDIS soaks up some rift energy. All right?"

"All right," she agreed, reaching for the door.

"Give my love to Sarah," he said quietly, in a rather peculiar tone.

Clara turned back and saw that he hadn't looked up from the console. "You could come with me, you know. She'd love to see you."

"Someday, perhaps, but not just yet."

"Don't keep putting off that 'someday,'" Clara told him seriously. "People age. Things happen."

"I know," he replied in a small voice. "Off with you, then" he added in a hearty voice that rang just a touch hollow. "Don't want to miss your train. Give K9 a skritch for me!"

"Doctor, he's metal. I'd break my nails!"