The numbers ticket back several seconds before the Doctor moved again, this time with total focus, all the admiration and curiosity drained from his face. He whipped out his sonic screwdriver and hunched over the console. "Let's see what's inside you." The sonic screwdriver emitted a barely audible whine as he held it this way and that, adjusting the tiny dials and switches. Finally they heard a CLICK and the Doctor stepped back just as a panel popped open.

"AH ha!" he said triumphantly, leaning over the opening. A yellow-orange light pulsed up, reflecting off his glass. "Uh-hu, yep, all rightly," he muttered, looking around. Then he popped back up, nodding to himself. "Just as I thought."

"Well?" asked Martha after he didn't continue.

"It's a bomb," he said matter-of-factly. "A real big one."

They all stood silent for a moment, taking this in.

Finally Jack said, "how big is 'real big'? Are we talking the block? The city? The country?"

"No, no," the Doctor shook his head, then ran a hand through his hair, scratching behind one ear and looking around. "I mean 'big' like the planet--
possibly the Moon. Actually," he cocked his head to one side, considering, "I wouldn't want to be on Mars when it goes off. Jupiter maybe, but still..."

"Doctor!" Martha cut in. "What are we going to do?" He whirled around as if he'd forgotten they were there.

"Oh, I'd think we'd want to disarm it," he glanced at the numbers, "and quickly would be best."

Jack went up to the console, peering at the buttons and levers. "There's got to be something here-- something we're missing. What do all of these controls do? You don't need anything this complicated to set off a bomb."

"You're right Jack," said the Doctor, seizing on the idea. He pointed the sonic screwdriver deep in the open panel. "There's something else in here," he said after a few seconds of fiddling. "Got it!"

The numbers floating above them suddenly shrank down to a fraction of their former size and a new display appeared in its place. A complex arrangement of shapes and equations, changing perspective every few seconds, numbers swooping in and out and occasional flashes of what looked to Martha like DNA helixes.

"I know this..." muttered the Doctor as he stepped back, starring intently at the display. "Why do I know this? Why? Why?" He started tapping the side of his head with a fist as if trying to dislodge the knowledge physically from the back of his mind. "It's something from a long time ago." He looked up, shock naked on his face. "A long time ago..."

"What is it Doctor?" pushed Jack.

The Doctor laughed, ignoring the question. "No, it can't be!" He sprang forward, looking at the controls again. "It can't be! No way!" He looked up at them, clearly mystified and delighted. "But it is!" His hands darted out across the buttons, lightening fast. The display swiveled and swirled and then resolved itself into a complex three-dimensional shape with various equations strung out around it. At the same time, the timer began to glow brightly and ticket forward several minutes.

The Doctor let out a whoop and banged the machine. "See! I knew it... but how..." he shook his head, still oblivious to the others starring at him. He froze, then suddenly sprung at Martha grabbing her by the shoulders. "But that's not the question is it? I should be asking 'why'? Why! Why, in all of time and space..."

"Doctor," Jack pulled him away from Martha, exasperation clear on his face. "Pull yourself together and tell us what it is? You gave us a few more minutes with-- with whatever it was that you did. But can you stop it?"

The Doctor took off his glasses and wiped his eyes. "Yes, yes, I can stop it. All I have to do is... win the game."

"The game?" Martha and Jack said at the same time.

"It's a game-- but not just any game," said the Doctor, putting his glasses back on and clearly switching to professor-mode. "It's a Timelord game. It's used to teach the basics of time-space manipulations." He shrugged, "Kid's stuff really," he threw them a glance and shrugged. "I mean, if you're a Timelord."

"So you win the game and the bomb will disarm itself?" asked Jack, shacking his head. "How stupid is that?"

Martha shook her head, "why would someone take a children's toy-- a Timelord children's toy-- and turn it into a bomb?"

The Doctor looked equally puzzled. "Yeah, that does seem really strange." He turned excitedly back to the device. "But I haven't gotten a chance to play with one of these in-- oh, 800 years or so." He waggled his eyebrows, "should be fun!" He sprang back to the console and the game started shifting and dancing again. A few seconds later he clapped his hands triumphantly and time glowed again. "Here we go," he said, rubbing his hands together as the display reconfigured itself.

But his hands didn't jump out across the console again, instead they fell limply at his side. Martha wasn't sure how a Timelord's circulatory system differed from a Humans, but two hearts didn't seem to keep all the blood from draining from his face.

"What wrong?" She asked, keep her voice low. "Is it different? Some other game?" She tried not to glance at the timer which had resumed its steady march towards zero.

"There's nothing I can do," he said, not taking his eyes off the display. "We're doomed."

"But you said-- you said it was just a game," she protested. "A game for Timelords. And you're a Timelord-- so play it! Doctor," she heard her voice rising to a plea, "you have to at least try!"

"It is a game for Timelords." He turned to face her, his usually fiery eyes empty, "but I'm only one. And it's locked... locked into multiplayer mode. I can't win it, not alone."

"Can someone else play it with you? Maybe Jack or-- I don't know, someone really smart, who knows about space and time and stuff..." she trailed off as he shook his head.

"Only a Timelord." He ran his hands along the controls. "Only a Timelord can see the ebb and flow of what's been, what's to come and... what has to happen. No one else can hold all of that knowledge in their mind at once." He starred off into space. I'm just not enough. I'm sorry."

Martha and Jack looked at each other helplessly, the UNIT staff buzzing with mummers just out of hearing. The Doctor seemed lost in thought, more alone than ever.

"Wait!" Jack lept towards him, waving a hand in the air. "You just said-- you need the mind of a Timelord. Well, there may be only one Timelord left in existence, but there is someone else who has-- who I had-- the mind of a Timelord." He starred meaningfully at the Doctor.

"No, no." The Doctor shook himself as he backed away from Jack and his suggestion. "I will not. I could not. Not her."

"But Doctor," Jack insisted, "if you don't, she'll die anyway. Along with the rest of the planet. We have to."

"Who?" asked Martha. "Who are you talking about?"

"He means Donna," said the Doctor flatly. "He means we need to wake up the Doctor Donna."