It took a bit of tracking down, but he eventually traced it. It had fallen into private hands at some point in the 21st Century, then it was donated to the Mission for the Preservation of Historical Artefacts a few Centuries later. Soon after that it was stolen, for the second time. Well, it was really the third time because no one really knows about the second time, except for him he supposes.
The first time it was stolen, a sticky-fingered Austro-Hungarian ambassador's son took from the Winter Palace as a souvenir of a royal conquest. How gauche.
The second time, a woman with too much time on her hands pilfered it for the twin reasons of; 'just because' and 'well, they stole it first'.
After the third time, it reappeared in the 52nd Century in the Royal Collection, on a stand and in a glass case that hadn't even been there before. "Out of thin air!" the tour guides would say with a flourish of their hands and fingers. Thin air indeed!
And when it came back it no longer opened and no one even remembered that it once did. Perception filter, ha!
That sealed it; he had to go and pinch it now. Not his fault of course, he was being led. Oh how he missed being led.
But then of course a complication arose, in the shape of his granddaughter.
"Ahem." Clio is leaning on the doorframe, legs crossed and arms folded, drumming her fingers.
"Ooh!" says the Doctor as his head snaps up, "How long, em, how long have you been standing there?" He straightens up.
"Long enough. Glad you decided against the cat suit, I have to say."
The Doctor laughs nervously
"So what are you planning to steal?" she asks as she blows her fringe out of her eyes.
"What? Why would I steal something? I'll have you know miss, cheeky, Clio, I've never stolen anything in my life!" says the Doctor incredulously.
She steps into the wardrobe and starts going through a few of the rails. She throws a black poloneck jumper at him. "There, put that on." She continues searching through the rails.
The Doctor pulls on the jumper and admires himself in the mirror, striking a pose. Smooth, he thinks.
"Clio? What are you doing?" he asks as he spots her in the mirror with something black draped over her arm, rifling through a pile of boots.
"Oh, I'm coming too. I'm not missing out on this."
The Doctor groans, but knows there is no point in arguing.
They are crouched in the shadows of the doorway. The Doctor peers around the corner and sees the case glowing under a solitary spotlight, and inside is the egg. He turns to Clio and conveys an elaborate code of hand gestures to her. She looks at him blankly. "What was all that?"
"Oh. You stay here and cover me."
"Sure," she says with a hint of an eye roll.
The Doctor gets to his feet and tiptoes out into the room, scanning for lasers and tripwires with his screwdriver. He hears a noise and he turns on the spot to see Clio standing at the case. She has her own screwdriver, which she spins in her hand, before winking at him and sonic-ing the case. It clicks open. He darts over to her as she opens the case and he shoos her aside.
"Could be a trap," he whispers.
He gingerly places his hand into the case, runs his it alongside the egg – gauging its size.
"When I say 'run', run," he says and she nods.
He moves his hand up and down preparing to swipe. One, two, "Run!"
He swipes at the egg and his hand collides with the side of the case, setting the alarm screaming through the museum. The lights come on, almost blinding them, and rendering their black garb entirely useless. He fumbles the egg but manages to trouser it awkwardly sending the case shattering to the ground. Sensing that he has nothing to lose, he kicks over the stand for good measure. He dashes to Clio who is waiting for him at the door.
"Move, move, move!" And they run back to the TARDIS.
Five minutes later, a security guard plods around the corner rubbing the sleep from his face.
"Alright, alright!" he shouts at the alarm, and turns the switch to shut it off.
He surveys the mess of shattered glass and overturned stand, and sighs.
"I suppose I'll have to clean this lot up as well!" he says and turns to go to find his sweeping brush.
"Now!" the Doctor says moving to the console and bringing them back into the vortex. He extracts the egg from his pocket and takes his screwdriver out to scan it. "Aha." He picks it up and weighs it in his hand, turns it and locates the clasp and gently prises it open. He plucks out a little note and turns it over. "Clio."
"Hmm?" says Clio on hearing her name
"No, Clio," he says as he turns the note to show her her name written on it in her grandmother's handwriting, "it's for you."
"For me?" asks Clio, baffled. He reaches out with it between his first two fingers and she takes it from him. He returns to looking into the egg, finding more treasure, which he hands to her. It's a cameo brooch, engraved on the back:
my darling granddaughter,
Clio's eyes widen and she turns it: River's profile in white on a pale blue background. Clio runs a fingertip over it. She then unfolds the note:
Happy Birthdays my beautiful girl. I hope you think of me when you wear this, the way I think of you every day. x
Clio's eyes well and she lifts them to look at the Doctor. She passes him the cameo and note.
"Hm," he sniffs after reading it and looks at Clio, one of her tears escapes the cage of her lashes and spills down her cheek.
"She knew? When she was here?"
"Nah, she figured it out much later," says the Doctor smiling, remembering.
Somewhere, River Song is aboard the TARDIS cradling her sleeping newborn son trying to summon the will to place him in his cot. She strokes his jet-black hair with an open hand. His little fists, which have been resting next to his face, twitch. His features scrunch before his eyes open and he looks up at his mother. She looks back down at him a little quizzically.
"What is it?" the Doctor asks.
"There is something so familiar about that look he's giving me."
"Everyone looks at you like that! And he's looking up at you and he can't believe that his mother is the Great River Song!" he laughs.
She snaps her head up. "What did you say?"
"The Great River Song?"
"Spoilers, sorry," she says with a grin.
He shakes his head at her. "Will you ever run out of spoilers for me?"
"Yes," she promises and kisses him softly.
Clio has gone to put her brooch and the note in her room, leaving the Doctor by the console still clutching the opened egg. He had noticed something more inside, but wanted to wait for Clio to be gone before taking it out. He reaches in now and pulls out a little blue origami whale.
"Hm!" he grins and turns it. He spots, in tiny letters on the tail of the whale: Open me!
So he unfolds the origami carefully and written in silver ink inside he reads:
Hello Sweetie x
He tucks it into his breast pocket, holding a hand over it for a moment, before carrying on.