Donna was still busy brooding about Lee when the Doctor popped up out of nowhere and launched immediately into a fast-paced monologue.
"Donna! The problem is worse than I thought. Definitely sabotage. We got through the computer system only to find the saboteurs had already beaten us to the propulsion sections and mucked up the maneuvering thrusters to the extent that they can't be repaired. The crew's working on getting spare thrusters out of storage now – how well prepared is that, having a full set of spare thrusters? - but swapping them out will take a good twenty minutes at the least, and meanwhile we're on course for the gas giant with no idea what they plan to do once we get there, and no way to know what other damage they might be doing in the meantime. How's your search going, by the way?"
Donna, brow still furrowed, hadn't looked away from her steady stare across the room at the door Lee had exited throughout this whole spiel. Bloody gorgeous wanker waltzing in and out of her life…
The Doctor blinked at her and leaned in close to her face. "…Donna?"
She started, gave a little gasp, and glared at him in annoyance.
"What?" she demanded. "I'm busy!"
The Doctor bounced impatiently on his toes and looked annoyed. "The saboteurs. Have you heard anything? They must have faked their identities to get onboard as passengers. No other way to board the ship, security being what it is. Well, except for us, we've got the TARDIS. Donna, I need your mobile!"
He held out his hand and twitched his fingers.
Donna looked down at his hand, narrowed her eyes in suspicion, and didn't move. "Why?"
"I'm going to turn it into a sort of temporary anti-biodamper by altering the frequency of the radiation it emits so that we can carry out a search of the ship for the fake passengers before they do any more damage."
"Why can't you use your phone?" Donna asked, still not budging.
"I would! I haven't got it on me!"
"Well, where is it?"
"I left it in the TARDIS."
"You left it in the TARDIS? What point is there in having one if you never carry it?"
"Donna, just—!" He pulled his hair in frustration. "Rose! Where's Rose?" He looked around wildly.
Donna leaned back in her chair and gave him a skeptical look. "I haven't seen her since we left the bridge, but she hasn't got her mobile either. No handbag. And trust me, I'd know if she was hiding it in her dress. That fabric doesn't hide a thing."
The Doctor suddenly spun back to her, alarmed.
"What? That was more than fifteen minutes ago. It doesn't take fifteen minutes to get out here from the bridge. Where else could she have gone?"
Donna crossed her arms. "She said she was going to the TARDIS. Perhaps she tried calling and left you a voicemail," she suggested dryly.
The Doctor, ignoring this remark, paced the floor, eyes scanning the room for any glimpse of blonde hair and wine-coloured fabric. Finding none, he came back over to Donna with exasperation written all over his face.
"Why does no one ever listen to me? Don't wander off, don't draw attention to yourselves, don't touch the glowing alien rock. Ten quid she's gotten herself into trouble of some kind."
Donna rolled her eyes. "Well, I'm not taking that bet. Can't the ship find her? Bio-scans or whatever?"
The Doctor darted over to an open access computer, quickly typed something, and then buzzed the sonic at it. "No. No bio-signs matching hers on the ship. The biodampers again, probably. She must have run across the saboteurs."
Donna hurried over behind him, now worried. "What? What'll they do? Wait, you can find her. Here's my phone—!" She pulled her little handbag off her shoulder and started to fumble through it.
"Don't bother, no time to tinker now," the Doctor interrupted. "And anyway, to find Rose, I don't need it." He was already holding his sonic screwdriver up to his face, squinting as he adjusted the settings, tongue poking out a little in concentration. Satisfied with the adjustments, he clicked it on with its usual blue light and high-pitched whirr. Using both hands, he slowly waved it side to side in a sweeping motion reminiscent of water dowsing, picked up on some sort of reading, and set off down the hall out of the dining room at a brisk pace. Donna hurried after him, concern written across her features.
"There are only two sources of huon radiation in the universe right now, both on this ship," he explained, "The TARDIS and Rose. And biodampers don't block huon. Remember when we met?"
"Pencil in a mug, how could I forget?" Donna smirked, running after him down the corridor. Neither of them remembered to call Shaun, left behind in the dining hall.
…
Donna and the Doctor traced Rose to the ship's water filtration and reclamation room, which was dimly lit with orange-tinted industrial lights and sported many big heavy-duty pipes all over the place. They snuck closer and peered round the door.
Inside, they saw a crewman – ship's security, it looked like – tied to a wheely chair with his head lolling drunkenly on his shoulders, being slowly pushed back and forth like a shopping trolley by a grey-bearded lizard man with a tall, oblong head. Two other crew members lay passed out on the floor beyond him – the technicians, in all probability. A second lizard man with a thin black goatee lounged in obvious boredom against a water tank a little ways to the right. The Draconians and the technicians all wore large green and black braces on their wrists. The security guard did not.
"Draconians," the Doctor whispered to Donna. "Usually quite honourable. I dunno what they want to sabotage the ship for. This is out of character for them. By the way, see the biodamper?" He tapped his wrist, indicating the wristbands. "Makes them practically invisible to the ship's computers. To bridge scans, it probably looks like security's walking back and forth, making its rounds as normal. Clever."
They peered a little more to the left, and saw Rose handcuffed to a folding chair, a matching biodamper clamped on one of her wrists. She was busy being cheeky to the guards.
"Oh, you think you're so clever hidin' down 'ere. Well, you better hide. 'Cos you're rubbish at sneakin' around, I can tell you. Seven decks on the ship, and you can't even do the research to learn what's on each one. Three words, and I pegged you, and I wasn't even lookin'."
The lizard men ignored her. Rose leaned her head back and cast her voice over to the right, to someone else who was apparently in the room out of sight of the door.
"You hear that, princess? Your goons here are idiots."
"Silence!" commanded an irritated female voice. There were footsteps, and an imperious-looking human woman with a tall forehead and a blonde beehive strode into view. "Your nattering does you no good, and tests my patience. If you will not cease, you will be drugged like your friend and made to be silent."
"Yeah, and what drug is that?" Rose asked warily, a little more cautious but still hoping to get some good information out of her.
"Keep talking, and find out!" the woman hissed. She whirled away.
Rose turned her attention to the tied up security guard, who had now been left to rest in his chair a few feet away from her.
"Hey," she said in a low voice to get his attention. "You alright, mate?"
He opened one eye dreamily. "Wha'?"
"Are you alright?"
"Who're you?" he slurred.
"My name's Rose. I'm here with some friends, and we're going to get you out of here."
"Out of where?"
"Out of this mess," she said, lips quirked up a little at the corners. "You're tied up in the pipe room."
"What pipe room?"
"On the Hindenburg. Your ship."
"My wha'? I have a ship?" He tried to get up, but the bonds held him. "Hey, why can't I move my arms?"
"You're tied up."
"Why'dja do that for?" he asked accusingly.
"I didn't! It was the lizard people," she said, starting to feel a little exasperated. She jerked her head in the direction of the guards, and the man looked, then widened his eyes in alarm.
"I don't remember no lizard people!" He looked around and started when he saw them. "What the—! What do they want? Where's Marcy?"
Rose didn't know who Marcy was, and decided it wasn't worth asking.
The Draconians huddled together to review some sort of message on a data-pad.
"Princess, our course is steady. Rendezvous with the outer rings will occur in fifteen minutes." The older Draconian saluted the beehive woman.
"Good," she replied. She reached up to her shoulder and pinched a button on her brooch that made her human skin and hair flicker and then vanish, revealing the lizard skin beneath. "It is time we left this hole and finished what we came for. Begin stage two!"
The older of the two male Draconians responded to this with an immediate formal bow. The younger gave a sullen glance at his companion and then made a perfunctory bow of his own. "Yes, Princess."
The younger moved over to a valve built into the main water pipe leading out of the filtration tank, and pulled a large injection flask out of his jacket. He opened up the valve and hooked the flask up to the input line.
"This will neutralize the crew and any passengers who might get heroic ideas about interfering with us," he said, opening it to inject the flask's contents into the freshly filtered water.
From their hiding place near the door, the Doctor and Donna watched this new development with dismay. Donna turned to the Doctor, worried.
"The put something in the water. What was that?"
"I don't know," he answered, "but that water is used all over the ship – taps, cooking, even for fuel. We've got to shut it off before it hits the propulsion section, or we don't know what it could do."
"Can you do that from here?"
"I'm gonna try. You go warn the captain and crew about the water – don't let anyone start drinking it or bathing in it. I'll free Rose and see what I can do from here about stopping the flow and reversing it back into the filtration tanks."
Donna nodded and took off running back down the corridor they'd come from, towards the stairs leading back to the dining hall.
Unnoticed by either her or the Doctor, the fourth saboteur, still in his mammalian disguise, was just stepping out of the engineering lounge on that level and saw her run by. His eyes narrowed, and he abruptly changed direction to follow her towards the dining hall stairs where she'd escaped.
Donna burst into the dining hall barely out of breath, and bellowed at the top of her lungs.
"Everyone stop drinking the water! It's been poisoned! There's something in it!"
Guests stared at her in shock. A concerned older woman turned and reached out a tentative hand toward her.
"My dear, are you all right? I do believe you're drunk!"
Ignoring her, Donna staggered over to the nearest buffet steward and grabbed him by the lapels.
"Listen, get up to the bridge and tell the captain or whoever to turn off all the water! It's been contaminated!" she ordered him.
He stammered at her, eyes wide. "W-What?"
"Don't gape at me like fish! GET MOVIN'!" she shouted. He stumbled backward and then took off for the bridge.
Around her, the other passengers had started giggling nervously and remarking over what a strange woman this was who had just popped in out of the blue and started yelling crazy things. The water had been poisoned? How absurd! This was a Minerva Cruiseline vessel! They had the best security in the galaxy!
The mood in the room was too light for her to be taken seriously. Donna whirled around, looking for Shaun. She found him still sitting at a table with his feet up on the chair next to his, lounging back with a wine glass in his hand. She marched over to him and with some surprise, was joined by Lee on the way.
Lee had slipped back down to the dining hall a few minutes earlier in a third attempt to collect some dinner, and was alarmed by Donna's sudden dramatic pronouncement. Instinctually, he found himself running over to her.
Donna looked at the two of them, her earlier strop forgotten, and said in an urgent tone, "The saboteurs have captured Rose, and they've put something in the water! We've got to stop these people drinking it!"
Shaun laughed a little sloppily, and held up his wine glass. "I hardly think anyone here's drinking water!"
Donna realized he was more than slightly sloshed, and felt a rush of annoyance wash over her.
Just then, she noticed a familiar face enter the room from the employee only corridor. He had a long, tapered forehead and his hand was hovering around a small black box on his belt as his eyes scanned the room for her.
"Oh, blimey!" she exclaimed, ducking suddenly. "That's one of them! Get down, get down, quick!" Pulling Lee with her, she dove under Shaun's table for cover.
…
So, I know Draconians in the show were originally very male dominated, but that was two or three thousand years before this takes place, so I'm playing it like their culture evolved during that time to be more gender equal. In fact, I'm also gonna just pull this historical retcon out of thin air here:
Sometime in the 48th century or so, a Draconian emperor died without a clear heir, leading to a dynastic war over two rival lineages, during which both legal male heirs died, and this all ended with the first female emperor of Draconia. She, too, had no male heirs, and so left the throne to her daughter, beginning a new tradition, and the throne has been passed down matrilineally ever since, until 50 years ago, when the empress died in the rings of K'ribb-dees, and a revivalist faction took over and placed a new male emperor on the throne instead of the empress's daughter. This is not particularly relevant to our heroes' perspective on events happening now so I won't bother explaining it in the actual story, but in case you were wondering, there it is.
TL;DR - I wanted a lizard princess who wasn't Silurian, so I made one up.