"Doctor!"
The Doctor turned to face his companions curiously. "What?"
Amy raised a hand; whatever was cupped within it was too small to see from across the ancient cavern, (well, ancient to the planet but just a hop, skip and a jump away from Amy and Rory's time—couldn't be much more than a hundred years later, at any rate) so he bolted across the room. Rory was peering over her shoulder as well, and extended a hand to it before Amy slapped it away.
"It's a ring," Rory said, wincing at the slap but saying nothing more about it. The Doctor peered in closely, an inch from Amy's hand.
"Well, of course it's a ring," he said, watching it carefully. The other two glanced between him and the ring curiously. Something seemed to be ticking in his mind, and he took a step backwards thoughtfully. "Somebody's been here just before us, or—and this is a very wonderful thought—is still here right now."
"D—Doctor?" Amy asked. "Who does the ring belong to?"
"To whom does the ring belong, Amy, respect the good grammar," the Doctor corrected, never once taking his eyes from the ring.
The woman groaned, rolling her eyes and grabbing Rory's sleeve, as if for support. "To whom does it belong, then?"
The Doctor began to smile. "To someone noble," he whispered, a small laugh escaping his lips. Amy and Rory suddenly blinked, looking beyond him. "Someone…so, so noble. And brilliant. And clever. And…you're standing right behind me, aren't you, Donna?"
He turned around, and his eyes met a face he'd never seen, but eyes only wise enough for one woman.
"Oi, watch it, Spaceman," Donna grinned.