Wish Bone, Funny Bone, Broken Heart

Except John tells him to go to his mind palace, and Sherlock tries, he goes through the motions, but the earthquakes have cracked the foundations and crumbled the walls and the shelves have toppled, spilling the contents everywhere, treasures crushed underfoot. Sherlock surveys the carnage with a despair bordering on panic. He opens his eyes. “I’m sorry, John,” he says. “I don’t know.”
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Sherlock has returned. Everything is fine. Except.