Let's write!

 Nyssa slowly made her way towards the TARDIS library.  To say the Trakenite was in need of a break would've been a valid assumption. Their most recent adventure had been to the Arctic in the 34th century. While that had been interesting (and more than a little cold),  it was getting pretty late and she was in need of something soothing.  As she trekked the long corridors, something on the floor caught her eye.  It was a round pale-green rock. More accurately, it was more of a geode shape, with grey crystal pieces sticking out the top.

How did this get here? Nyssa thought, holding the sphere close. 

Then, she began to hear it.  A whisper.  Soft at first, but as she touched the sphere again, it grew louder before Nyssa realized it sounded like her own voice.

"Adric, I can't see Traken" came the whisper. 

Nyssa was stunned.  Why would she hear her own voice, her own memory?

A second later came another whisper, and with it a flash of light on the corridor wall.

"-Cybermen yet. We can stop it before it gets too far!"

"No!" 

Nyssa nearly jumped out of her skin at that. That argument had happened only recently, But how did it...?
Grasping the sphere tightly, she ran to the control room.

The Doctor stood at the console, staring at the screen as his hands automatically flitted around the buttons.
"Ah, Nyssa!" he called, seeing his companion walk in "There you are, I was wondering if you could-"

"Doctor" she began, cutting him off. "I found this on my way to the library. " She held out the pale green object. "I believe I know what it's for."

The Time Lord looked concerned. "Oh, you found it."

"Yes" said Nyssa, "It's some sort of...recording device. Like the cas-sette player Tegan had."

"In a way," the Doctor confirmed. "It's called a Kallitan Memory Keeper.  The Kallitans are a semi-telepathic species but they don't exactly have the best memories. This lets them keep all their memories stored for later-the good and bad."

"But why would you be concerned if I found it?"

"Nyssa, this device is telepathic. Whoever holds it leaves their memories and mind free for accessing. I suppose you noticed the star bursts?"

"Star bursts?" she asked "You mean the flash of light before it plays a memory?"

"Exactly" the Doctor answered "A tiny fragment of memory reacting with the elements in that sphere produces a burst of energy released. Quite painful if one is unprepared."

"A kind of chemical reaction?"

"Yes. And given your abilities..."

Nyssa nodded in understanding. As she turned to leave, a thought came to her. 

"Doctor?" she asked softly "What sort of memories do you keep in it?"

The rest of the evening the time travellers sat in the console room, the lights dimmed, as the Doctor held the Memory Keeper in one hand, and listened to the myriad of whispered voices.

"Grandfather!"
"...Which have bred the most terrible things!"
"You don't mind, do you?"
"Oh, you shouldn't be worried. A Time Lord has ninety lives."

And with each whisper came another burst of light, until the wall looked like a sea of shooting stars.

(Lifetimes Later, But Centuries Earlier)

They were all gone.  He was once again a man in a box; only this time parked on a cloud in London. The boyish Time Lord reached into a pocket, pulled out a nearly-forgotten pale green sphere, and sat bathed in the memories of his friends. So many adventures, so many memories bursting like shooting stars.