"We've stopped." Val said. "Have we stopped?"

"Are we there?" Biff asked.

Groaning, Luna lifted her head from her knees where it had been resting before glancing over the Doctor who smiled at her.

"Rise and shine sleepyhead," he murmured, brushing a stray lock of hair away from her forehead.

"I'm called Luna… That implies the moon which means night time! Lemme sleep!" she complained, putting her head back on her knees so she could sleep though, while she was waiting to drift off, she continued to listen to the conversation.

"Are we there yet?"

"We can't be, it's too soon." Dee Dee said.

"They don't stop, Crusader vehicles never stop." Hobbes said.

"If you could just…return to your seats." The hostess said, walking to the intercom. "It's…just a small delay."

"Maybe just a pit stop." Biff said.

"What's going on?" they heard the hostess ask.

"There's no pit to stop in." Hobbes replied. "I've been on this expedition 14 times, they never stop."

"Well, evidently, we have stopped, so there's no point in denying it." Sky said.

"We've broken down!" Jethro said laughing.

"Thanks, Jethro." Val said sarcastically.

"In the middle of nowhere!" Jethro continued.

"That's enough, now stop it!" Biff ordered.

The hostess walked back to talk to them.

"Ladies and gentlemen and variations thereupon," she said. "We're just experiencing a short…delay, the driver needs to stabilize the engine feeds. It's perfectly routine, so if you could just stay in your seats…"

Growling, Luna was pulled to her feet by the Doctor before being dragged to the front of the shuttle, towards the driver's cabin.

"No, I'm sorry sir, miss," the hostess said. "I…could you please…"

"There you go, engine experts!" the Doctor said, motioning to them both. "Two ticks!"

Without allowing the woman to speak against, he pushed through and into driver's cabin.

"Sorry, sir, if you could just sit down!" the hostess protested. "You're not supposed to be in there…"

The door closed behind them.

"Sorry, if you could just return to your seats, sir…" the driver said.

"Howdy… We happen to be from the insurance department… Y'know what businesses are like, always wanna make sure their ass is covered," Luna began, ignoring the look she got from the alien beside her. She didn't really like to swear but if it helped to create a 'character', she would do it.

"Let's see if we can get an early assessment." The Doctor continued. "So, what's the problem, Driver Joe?"

"We're stabilizing the engine feeds, won't take long." Joe replied.

"Liar… That little light there's the engine feed and it looks fine… no blipping and bleeping in sight so onto the next excuse…"

"Plus it's a micropetrol engine, so stabilizing doesn't really make sense, does it?" the Doctor said. "Sorry! I'm the Doctor, I'm very clever."

"And I'm Luna, just as smart and so much more modest."

"So, what's wrong?" the Doctor asked.

"We just stopped." The other man in the cockpit told them. "Look, all systems fine and everything's working, but we're not moving."

Pulling out his sonic, the Doctor began running it over the panel.

"Yeah, you're right." He said. "No faults. And who are you?"

"Claude." The man answered. "I'm the mechanic. Trainee."

"It's lovely to meet you Claude," Luna said, shaking the man's hand kindly. "Enjoying being a trainee?"

"Aye, it's not too bad…"

"So, what'd you do to kill the boredom 'round here? Eight hours is a hell of a long time."

"Well-"

"I've sent a distress signal." Joe interrupted. "They should dispatch a rescue truck, top speed."

"How long till they get here?"

"About an hour." Joe replied.

"Well, since we're waiting…shall we take a look outside?" the Doctor asked. "Just…lift the screens a bit?"

"It's 100% Xtonic out there." Joe told them. "We'd be vaporized."

"No, those windows are Flintoglass, they'd give you a couple minutes." The Doctor said. "Go on! Live a little!"

Joe gave in and pressed a button. The shield rose and the four of them stared in awe.

"Look at all those diamonds!" Claude marvelled. "Poisoned by the sun. No one can ever touch them."

"Joe, you said we took a detour?" the Doctor said.

"Just about 40 kliks to the west." Joe replied.

"Is it a recognised path or did you just decide to wing it?" Luna asked, tilting her head to the side with a sickly sweet smile.

"No, it's a new one." Joe replied. "The computer worked it out on automatic."

"Did you just…?" Claude said suddenly. "No, sorry, it's…nothing."

"What'd you see?" The red haired woman asked.

"Just there." Claude said, pointing. "That ridge. Like…like a shadow. Just, just for a second."

"What sort of shadow?" the Doctor asked.

An alarm began to sound.

"Xtonic rising!" Joe said. "Shields down."

"Look, look, there it is, there it is!" Claude said, pointing frantically as the shield descended. "Look, there!"

"Where?" the Doctor asked. "What was it?"

"Like, just, something….shifting." Claude struggled to describe. "Something sort of…dark. Like it was running."

"Running which way?"

"Towards us…" Claude replied, trailing off.

"For God sake! How come, whenever we go on holiday, something bad happens! A weird shadowy thing is running towards us and we have no idea what it is…"

"Right, Doctor, ma'am, back to your seat and not a word." Joe told them. "Rescue's on its way. If you could close the door, thank you."

The Doctor and Luna made their way out of the drivers cabin and went to join the other passengers on board.

"What did they say?" Sky asked. "Did they tell you? What is it, what's wrong?"

"Oh, just stabilizing." The Doctor told her. "Happens all the time."

"I don't need this." She said. "I'm on a schedule. This is completely unnecessary!"

"Back to your seats, thank you." The hostess said.

The alien couple moved to their seats, chatting quietly, while the hostess made her way up to the cockpit.

"Excuse me, Doctor, but they're micropetrol engines, aren't they?" Dee Dee asked in a low voice, leaning forward.

"Now, don't bother the man." Hobbes told her.

"My father was a mechanic." She continued. "Micropetrol doesn't stabilize, what does 'stabilize' mean?"

"Well." The Doctor said. "Bit of flim-flam. Don't worry, they're sorting it out."

"So it's not the engines?" Hobbes asked.

"It's just a little pause, that's all." The Doctor replied.

"How much air have we got?" Hobbes demanded.

"Professor, it's fine." Dee Dee told him.

"What did he say?" Val asked.

"Nothing." The Doctor replied.

"Are we running out of air?" the woman demanded.

"I was just speculating…" Hobbes said.

The hostess walked out of the cockpit.

"Is that right, miss?" Biff asked her. "Are we running out of air?"

"Is that what the Captain said?" Val asked.

"If you could all just remain calm…" she replied.

"How much air have we got?" Val demaned.

"Mum, just stop it." Jethro told her.

"I assure you, everything is under control." The hostess told them.

"Well, doesn't look like it to me!" Biff said.

"Well, he said it." Val accused.

"…it's fine, the air is on a circular filter…" Dee Dee was trying to say.

"…he started it…" Val continued.

Everyone just started talking at once.

"Shh!" the Doctor tried. "Shh!"

"FINGERS ON LIPS!" Luna yelled, putting her finger to her mouth and staring at the other passengers until they all followed suit.

"Thanks for that… Now, if you'd all be so kind as to shut your pie holes and turn your attention to one of the 'variations upon', you might actually get the answers you're so desperately searching for."

"Um, thank you." He said, looking at his lover for a few seconds, dumbfounded before speaking again. "Now, if you'd care to listen to my good friend Dee Dee…"

"Oh!" she said, surprised by the sudden attention. "Um…it's just that…well, the air's on a circular filter so…we could stay breathing for ten years."

"There you go!" the Doctor said. "And I've spoken to the Captain, I can guarantee you, everything's fine."

They heard two knocks on the wall.

"Do you have paid actors hanging around, waiting for those words? Or are you just that unlucky?" Luna muttered, remembering the dozens of times that he said 'everything's fine' before the situation took a turn for the worst.

"What was that?" Val demanded.

"It must be the metal." Hobbes told them. "We're cooling down, it's just settling…"

"You're one of those dudes who are scared when they're alone, aren't you?" Luna asked, looking at the professor with a smile creeping onto her face.

"Excuse me?"

"You know, when you're sat in bed and you can hear footsteps. You just rationalise it away and blame the pipes so you can sleep at night. It's quite endearing professor… to think, with all that knowledge you have, you're scared of what goes bump in the night."

"Looney, that's enough," The Doctor told her, not wanting her to start an argument with the older man.

"Rocks." Dee Dee suggested. "Could be rocks falling."

"What I want to know is, how long do we have to sit here?" Biff asked.

The knocking was repeated, still just two knocks.

"What is that?" Sky asked.

"Is someone out there?" Val called.

"Now, don't be ridiculous!" Hobbes said.

"Like I said," Dee Dee told them, "it could be rocks."

"We're out in the open." The hostess said. "Nothing could fall against the sides."

The two knocks came again.

"Knock knock." The Doctor said.

"Who's there?" Jethro and Luna said at the same moment.

"Is there something out there?" Sky called. "Well? Anyone?"

It knocked again.

"What the hell is making that noise?" she demanded.

"I'm sorry, but the light out there is Xtonic, that means it would destroy any living thing, in a split-second." Hobbes told her. "It is impossible for someone to be outside."

The knocking repeated.

"Well, what the hell is that, then?" Sky demanded.

The Doctor pulled out his stethoscope and put it on the wall where the last knocks had come from.

"Sir!" the hostess called. "You really should get back to your seat."

"Hello?" the Doctor called.

The knocking came from the rear of the bus, near the fire exit, this time.

"It's moving…" Jethro pointed out.

The door began to rattle like something was trying to open it.

"It's trying the door!" Val called.

"There is no 'it', there's nothing out there." Hobbes told her. "Can't be."

Something rattled the door again. Then it began to move-always knocking twice-around the bus from the roof to the side door.

"That's the entrance." Val said. "Can it get in?"

"No, that door's on two hundred weight of hydraulics." Dee Dee replied.

"Stop it." Hobbes told her. "Don't encourage them."

"What do you think it is?" she asked him.

Biff went to the door.

"Biff, don't…" Val said.

"Mr. Cane, better not…" The Doctor said.

"Nah, it's cast iron, that door…" Biff replied.

Biff knocked on the door three times and the thing outside knocked three times.

"Three times!" Val said. "Did you hear that, it did it three times?"

"It answered!" Jethro marveled.

"It did it three times!" Val continued.

"All right, all right, all right." The Doctor said. "Everyone, calm down."

"No, but it answered." Sky said. "It…answered. Don't tell me that thing's not alive, it answered him!"

The thing knocked three times again.

"I really must insist you get back to your seats!" the hostess told them.

"No!" Sky yelled at her. "Don't just stand there telling us the rules! You're the hostess, you're supposed to do something!"

The Doctor walked to the door and knocked four times.

The thing responded with four knocks.

Sighing, the Gideon walked over to the Time lord and dragged him back a few feet, not wanting him too close to a potentially dangerous situation.

"Don't suppose you can try and be careful, could you? I can't fly the TARDIS and, as much as we like it here, me and Donna don't wanna be stuck at the hotel for the rest of our lives."

The thing knocked again.

"What is it, what the hell's making that noise?" Sky yelled, beginning to panic. "She said she'd get me. Stop it, make it stop, somebody make it stop! Don't just stand there looking at me, it's not my fault, he started it with his stories…"

"Calm down!" Dee Dee told her.

"…and he made it worse…" Sky continued raving.

"You're not helping!" Val yelled at her.

"…why couldn't you leave it alone?" Sky demanded. "Stop staring at me! Just tell me what the hell it is!"

"Calm down!" Dee Dee yelled.

The knocking became continuous. In her panic, Sky began backing towards the cockpit doors, the knocking following her.

"It's coming for me." She said.

"Ohh, it's coming for me, it's coming for me…it's coming for me! It's coming for me!" She screamed and the Luna moved towards her, her arms outstretched in an attempt to reach the older woman.

Suddenly, the whole shuttle began to rock violent and lights went out; the darkness was filled with sparks which hit the female alien, causing her to hiss in pain until the Doctor yanked her back, shielding her as much as possible while the passengers screamed around them.

Then, everything stopped.