She points at the brass key. "What is this?"

"This, Sarah, is a key to time." The Doctor strides down corridors that wind through the TARDIS. A door opens onto an endless expanse of grass beneath a bright sky. The Doctor's scarf flutters in the gentle wind.

The path from the door is lined with pedestals holding time-measuring devices, including an hourglass, a porcelain Sevres clock, a silver egg with glowing blue glyphs, and a sundial.

The Doctor approaches a cherrywood mantel clock. He inserts the key in the back, winding it carefully. "A Time Lord's work is never done."