After a lengthy search around the neighborhood, they find Susie leaning against the wall of the Doctor's TARDIS. Her palms are flat up against it and her eyes are shut, making the little girl in overalls and a bowl haircut an incongruous figure, yet one that seems to be trying to meld with the ship.

"Susie Derkins, I have some questions for you," the Doctor says, squatting down.

Something's off about Susie. Then Martha sees it and nudges the Doctor. "She hasn't got a shadow."

Susie stays facing away from them, shaking like she's holding back tears. "Calvin and Hobbes, sleep."

Calvin immediately slumps to the ground unconscious, flopping onto Hobbes who has been rendered into an inert toy again. Then they slowly fade away.

"What have you done to them?" The Doctor grabs one of her shoulders with his hand not carrying the screwdriver, and then steps back, aghast, when she's facing them.

"I sent them safe to their beds." This little girl, who looks like she's six, has eyes filled with golden light. The glow now emanates from her fingertips, every thrumming bit of skin.

"No. You couldn't be. You mustn't be."

"Doctor," Martha asks quietly, "have you seen this before?"

"When Rose bonded with the Time Vortex. But this would have killed a little girl. It killed me."

Susie gave them a sad smile. "Three of us together. Running from the War. But we crashed. Hobbes was crushed under a roof beam. The Esquire was burned in the fire. And I, in trying to repair the damage, fell unprotected into the Heart. I make sure The Esquire and Hobbes can't see it. Everyone else is a projection of The Esquire's subconscious."

"Did you give Hobbes the idea to call me?"

Her small hand sought out the Doctor's. "You may not be able to help, and there's so little of me left, but I am glad to see you again, Grandfather."

The Doctor stared, slack-jawed, for a few seconds, and then he scooped her up and nearly crushed her in his arms. "Susan…my Susan…"

"It's been so long, Grandfather…and I'm only alive in this simulation…and the power is draining from the ship…"

Kissing her forehead, the Doctor said, "Take me to the real ship, and I'll see what I can do."

Though Martha had not been warned about any of this beforehand, the thought of him being reunited in some small way with one of his family was making tears well up as she followed them back towards Calvin's house.

…

What was really exiting a constructed virtual reality seems every bit like crawling into large cardboard box with TRANSMOGRIFIER DUPLICATOR TIME MACHINE written on the side.

"He remembers bits of himself, just like you did," Martha says when they dig the cardboard box out

"I don't let him really use it," Susie says. "He uses his imagination instead. Such a mind he has…"

"Were you lovers, Susan?"

She smiles coyly. "It was a three-way relationship." And with this startling remark she disappears into the cardboard box.

"Did you have many grandchildren?" Martha blurts out just as the Doctor was stepping in.

"Susan was the best." When she sees his facial expression, she knows that is all he will ever give her.

Faint, yellow auxiliary lights illuminate in the gutted TARDIS. It looks like a burned-down toy store, with posters of circuses and amusement parks from a thousand worlds and times hanging in tatters, model dinosaurs and all sorts of alien dolls she's never seen before.

When they are here, Susie appears to be a tall, thin young woman with short brown hair and a gray business suit. The glow still fills her eyes and crackles the space around her. "I can't stay in reality long. I only had five or so hours to live when I started. Time in the simulation is slowed down. Calvin has been six years old for many years now."

"Where's your med bay, sweetheart?" The Doctor asks, and it is the most tender tone of voice Martha has heard anybody use, much less the Oncoming Storm.

Susie wraps an arm around his and leads them to it.

Hobbes is utterly broken, his spine cracked and deep gashes under singed fur. The Esquire – who does indeed have spiky blond hair that seems to require whatever hair gel the Doctor uses - is lying wrapped in a sheet, floating on some kind of gel, and with a medley of tubes and wires stuck in his chest and head. On the other end the tubes are drawing power from the ship itself.

The Doctor buzzes his screwdriver over The Esquire. "You did a brilliant job. His cells are reconstructing steadily. He'll be at full capacity again in…oh…fifteen years?"

"That really is Hobbes' mind in that childhood he's leading. I thought he deserved extra time."

"You're worried you'll run out of power before he's done, yeah? I can fix that for you." Then he puts a hand on either side of her face. "In fact, I can rig it so that all three of you can stay there permanently if you choose. You and Hobbes will have the option of true death. Not sure if you want that, but the choice will be there. Since you'll be controlling the simulation in the absence of another Gallifreyan mind, once the Esquire has left, you will also have the option of 'growing up'. I'll leave the Esquire a subconscious message letting him know what waits for him once he's healed, and he will be able to wake into reality and fix the ship, going out into the universe again. All he'll have to do is speak a code phrase. I'll even give him my phone number so he can look me up."

This time, it's Susie who wrapped him in a hug. "I love you, Grandfather. All these years I've wanted to say that."

"I…I love you too, Susan."

"And you. Martha. Make sure Grandfather doesn't get into more trouble than he can handle, please."

Martha accepts the hug with equal mesures awkwardness and satisfaction. Since she can't really help fix the ship, she goes and wakes up Calvin and Hobbes and they trade stories about their adventures through time, space, and imagination. They play Monopoly, and Martha is amused by Hobbes' invented strategy of robbing the bank. Martha gives a stern talking-to to the monsters under the bed, earning Calvin's eternal esteem, and she puts up with his incorrigible curiosity about disgusting diseases.

While Calvin is in the bathroom, Hobbes tugs Martha's sleeve. "I've just realized that I'm dead. The block's been removed."

Martha strokes his fur. "I'm sorry. But you can stay here with Susie as long as you like. Calvin might leave you, though."

He sighs, an elegant cat-sigh. "I don't want him to give up on life just cause he'd have to live without the two of us. There's a lot of good he can do."

"You are the best friend anyone could hope for, Hobbes."

This hug is not awkward, but it makes something catch in Martha's chest.

An hour later – four hours having passed since the Doctor said private goodbyes and sent Susie "home" - Doctor promises Calvin that he'll send them a letter saying Hobbes is a vital therapeutic presence in Calvin's life. Calvin runs off to catch fireflies in the backyard with his best friend.

Back in the Doctor's TARDIS, the Doctor asks Martha one question and she asks two.

"Still want to go home, Martha?"

"I'm glad I came this time, Doctor, but yes. Did you travel with Susan the way you traveled with me?"

"She was actually the first person I went traveling with at all."

"Out of curiosity, what is the code phrase Calvin can say if he's ready to be the Esquire?"

The Doctor grins and pulls a lever, sending them off. "'Let's go exploring!""

…

Author's Notes:

Susan (sometimes called 'Sailor Gallifrey'): first canonical Classic Who companion. She was the Doctor's granddaughter, though almost nothing else of the Doctor's family is known. Masqueraded as a British schoolgirl. I haven't actually seen any of her episodes, but I do a lot of research.

Some of this fic was inspired by the fact that CAL in "Silence in the Library/Forest of the Dead" reminds me of Susie Derkins as well as Calvin. Little brown-haired girl; loves books. With a similar name to Calvin's, she has supposed delusions that are in fact reality, while it's her reality that is artificially constructed.

And for those of you who haven't read every single C&H strip, "Let's go exploring!" is the last thing said in the series, as Calvin and Hobbes sled off into the wild snowy yonder. It sounds like something the Doctor would use as a code phrase, isn't it?