There's a softness in his eyes, the kind that's gentle with just a touch of that ancient sadness. He tugs at the collar of his shirt, runs his fingers through his already mussed hair, and tucks his sonic screwdriver in his coat pocket. He turns and looks back at the TARDIS, and there she is. His pink and yellow girl, poking her head around the door, her tongue tucked between her teeth in the grin that is so completely hers. She says something clever, but he misses it. He's too lost in her eyes.
And then he blinks and she's gone.
And he's alone. He adjusts his bowtie.
A moment later, another head pops out of the eternal blue box, but this one is too red, too tall.
"Doctor, what's taking you so –" But she stops when she sees the look in his eyes. "Doctor, are you all right?" He smiles and the softness is gone, hidden once again behind the bubbly child-like façade. The one that keeps him safe.
"Yes, fine!" He sweeps past the red one into the TARDIS and swaggers around the console, flipping switches. "Where to next, eh? The purple planet of Canten? Or the orange mountains of the Axilflount moon? Places to see! Come along, Pond!"
The blue box swirls through the time vortex, and the red one clings to the console.
The Doctor laughs to convince her, but in his mind's eye he still sees it. A flash of pink and yellow by the TARDIS door.
He blinks and it's gone.