"No."

The word is out of his mouth before he can quite comprehend what Dex is asking.

"Doctor-"

"No." Is that his voice? It is harsh and sharp, rings with finality. Nothing in all of the universes could convince him to return with Dex to Karphelox; in fact, he's pretty sure Dex won't be leaving the TARDIS anytime soon.

Dex's eyes are large and suspiciously wet, and his face is full of guilt. "Doctor, please. Just let me-"

"No." This time, the word is quiet, nearly a whisper. The Doctor turns away from Dex, cannot look him in the eye. He doesn't understand what could possess Dex to want to return to Karphelox. Everything in him rebels at the very thought, and he is having a hard time forming words.

Dex allows him the moment, doesn't speak, just slides closer and waits. The Doctor can feel his body heat against his skin; such a simple thing, but it nearly undoes him. He leans his head in his hands and wraps his fingers in his hair. "Dex, why?"

Dex pulls his good leg toward him and stares intently at his toes. "I messed up," he says, so softly that the Doctor nearly mishears him. A fat tear rolls down his cheek, and he wipes it away furiously. The Doctor feels his hearts clinch.

Dex sniffs. "Torren and Elliot, my friends, got captured by Eleazar's guards." He shakes his hair out of his eyes and continues in a whisper, "It's my fault."

The Doctor ducks down and carefully looks Dex in the eye. "It's not your fault," he says fiercely, squeezing his hand.

"But it is!" he cries, voice high and thin with desperation. "I never checked for an alarm in the power supply building!"

His eyes are wide and shining, and the Doctor is suddenly overwhelmed by thick waves of love for this little boy. He rests his hands on Dex's shoulders. Dex's won't meet his eyes. "Dex, look at me," he says, gently, firmly.

Dex reluctantly raises his gaze. His eyes are swimming with tears. The Doctor thinks that he'd do anything to have his smiling little boy back. "Sometimes," he says slowly, voice low and serious, "bad things just happen, and nobody can stop them from happening. You couldn't have saved them, Dex. Sometimes, we just have to accept it."

Dex blinks, and his gaze hardens into steely determination. "You're wrong," he says flatly, gazing at the Doctor with intense green eyes. "I could have disabled the alarm if I weren't so excited about using my sonic for the first time. It was a stupid mistake, my stupid mistake, and I don't have to accept it! We have to go back."

It is so like her, the stubborn glare and the endless loyalty and the flat refusal to compromise. The Doctor suddenly feels it all, like a slap in the face, everything that he'd lost, could have lost. It is far, far too much, and he nearly breaks. "Dex, we can't go back," he says roughly, eyes glittering with the pain of a thousand memories.

Dex is having none of it. "Why not?" he demands hotly.

The Doctor snaps. "I almost lost you!" he shouts, pulling away from Dex and running his hands fiercely through his hair.

Dex can see the panic in his eyes; the effects of the past three days have leaked onto his face, are written in the slump of his shoulders and the tension of his body. Dex hates it; he slides closer and bumps shoulders with him, gently. "But you didn't," he says softly, hoping to remind the Doctor that all of the might-have-beens in the universe pale in the face of this one simple reality. He is right here.

The Doctor feels a tremor run through his body at the contact, wants to cling to this little boy and never let go, feels a stab of guilt and shame. "But I could have, Dex," he nearly whispers, head is his hands. He looks at Dex now, eyes glittering, face haunted. "Do you know what he wanted to do to you?" he spits, voice rising. "He wanted to break into your mind and remove every single thing that makes up you, he wanted to slowly drain it out of you, all of your energy, that spark of life. He wanted to steal it, to hoard it all away and use it to enslave other children!"

Dex gazes at him. His hair is disastrous, standing up erratically, still matted with dried blood, eyes frantic, face pale and hollow. He looks half-mad. Dex thinks he's never loved him more. He wraps his arms around the Doctor and leans into his chest. "I know," he says softly, though he actually hadn't. It doesn't matter. "But I'm right here, and I'm not going anywhere," he says firmly.

The Doctor shudders involuntarily. He vividly remembers Rose telling him the same thing, nearly word for word, only days before Canary Wharf. He wants so badly to believe Dex, doesn't quite understand just why he needs this little boy, decides resolutely that it doesn't matter. He shake his head. "Dex, I'm scared." The words pass unbidden through his lips, voice raw and cracked, nearly a whisper, and for a moment he can't believe he's spoken. He's never been so honest in all his lives, and that scares him, too.

Dex thinks nothing of it, just takes a hand a squeezes it gently. "S'okay," he says softly. "I am, too."

The Doctor nearly laughs. It is absurd, this seven year old child that makes him say and feel and do things that he'd never dreamed in all of his lives. He shakes his head in amazement and decides that he wouldn't change it for all of the worlds.

They are silent for a long moment. Finally, Dex gently nudges the Doctor with his shoulder, jarring him out of his thoughts. "You need a shower," he says, wrinkling his nose slightly. "We can talk about it later, yeah? Time machine an' all."

"Oi!" The Doctor nudges Dex back and cocks an eyebrow at him. "So do you."

Dex grins at him and shifts forward in an attempt to slide off the bed. The Doctor grabs his shoulders and pulls him back. "Where do you think you're going?" he laughs.

Dex looks at him, perplexed. "Shower?"

The Doctor shakes his head as he rises and crosses the room. "Not like that, you're not." Dex can hear him rummaging around in a supply closet, hears a clatter and a muttered curse. The Doctor returns triumphantly carrying a silver pair of crutches.

Dex wrinkles his nose. "Really?" he whines.

The Doctor shoots him a confused glance. "You expected something different?" he asks, trying not to grin. Dex isn't fooled. He can see the amusement sparkling in those warm brown eyes.

Dex groans and rolls his eyes as the Doctor pushes the crutches toward him. He had been expecting something different. He slides off the bed and leans on them, testing. They don't hurt his arms as much as he'd anticipated. "S'pose it's better than being carried everywhere," he mumbles, and the Doctor laughs.

Dex turns back to the Doctor at the door of the med bay. "Doctor?"

"Hmm?" He is powering down the monitor.

"I won't forget," Dex says seriously.

The Doctor sighs heavily and turns to Dex. He is leaning on his crutches in the doorway, small and vulnerable, luminous eyes wide and hard with resolve. "I know," he says quietly. "But Dex, lets wait until you're better. Please."

The Doctor can see that Dex wants to argue, but reason gets the better of him. "Okay," he says after a moment.

The Doctor smiles softly at him, and Dex haltingly makes his way to his room. A shower sounds nice.