It did not take long for the Brigadier to return, and when he did, he had instructed his men back at UNIT headquarters to arrange the meeting of a small division with him and the trio at the warehouse. Harry quickly hurried back to the lab to gather the notes and instruments he had brought with him – as well as any leftover evidence of the Doctor's existence, while at the same time, Sarah ran back to the patient's room to fetch the glowing fob watch they had accidentally left unguarded. One might be able to image the small shock she got when she found the velvet pouch to be missing. But thankfully, her fright didn't last very long. Along with the TARDIS key, the fob watch had found its way back among the Doctor's belongings, who, in order to answer her question, had produced the pouch from the pocket of his jacket. For a moment, Sarah wondered whether she should try to question him about it again, especially about the glow emitted from the inside of the watch, but she decided to keep quiet. Only his old self would know the answer to these questions, and as he had stated himself a few minutes back, he was by far confused enough already. But there was only one thing she, and he, really needed to know about it, anyway: It was important. Never mind why, but it was very, very important in regard of the Doctor's true identity.
Once the Doctor, Sarah and Harry had left the hospital, they took the Doctor's black Daimler taxi to follow the Brigadier to the warehouse they had spoken about. Hours upon hours before, when the ambulance had taken the unconscious half-Time Lord away, Sarah had driven his newly bought, but battered car after them. She most certainly wouldn't have done that had she not thought that it was necessary at the time, because not only did the car look beaten, but driving it was about three times as bad. Nothing was working quite as one would expect it and she had accidentally taken off the knob on the gear stick twice. So, naturally, she quietly let out a sigh of relief as the Doctor insisted on driving and Harry did not argue.
On their way to the outskirts of London the rain kept prattling on the car's roof and during the one hour drive, the sun began to set behind the horizon. The overcast sky seemed to make the evening even darker than usual. Sarah found herself thinking about how long and stressful this Sunday had been so far.
Eventually, they arrived at the end of an old industrial park. The warehouse, their destination, loomed large in the distance. Its massive square structure and dimly lit windows had something threatening about them, causing an uneasy feeling within the young woman as friends and UNIT members drove up to its gates. On a week end's evening it was only common that no employees were around, but the absence of any other people except for the hired support by UNIT, just added to the slightly ominous atmosphere. There was no one and nothing to stop them from entering the terrain surrounding the warehouse. After parking in front of the staff entrance, they stepped out of the car and back into the rain, which had thankfully let up a little in the meantime.
Several yards away from them, the Brigadier, too, had left his car and was exchanging a few words with the UNIT soldiers waiting in a van nearby. They must have arrived a little earlier than the rest of them.
"I must say, I am not particularly thrilled to break in there...", Harry said quietly while he was standing next to Sarah and looking up at the faint glow emitted from behind the building's windows. "Do you suppose that someone's still at work?"
The young woman studied their surroundings carefully. Behind the corner of the building, a black car other than the Doctor's was parked. Because of the rain impairing her view and the darkness setting in, she had failed to notice it until now. "It's possible we're not alone...", she replied, then wondered: "… But what would anyone want out here on a Sunday?"
"Maybe the Doctor isn't the only one who's gotten cabin fever and came here to work...", Harry mused quietly, but not quietly enough.
The Doctor glared over his shoulder at Harry, displeased to hear him making such unsubstantiated assumptions. "I very much doubt that.", he told him.
It was about that time, that the Brigadier rejoined the trio. "Well then, shall we?", he asked and nodded in the direction of the staff entrance, before leading their little party towards the building. Since he had also noticed the light inside of the building, he knocked politely in the hope to receive an answer from whoever or whatever was inside. Yet all that followed the hollow sound of his knocking was the everlasting white noise of the rain on the tarmac and tin roof. The Brigadier raised an eyebrow and shot his companions a glance as though he was asking them whether someone had a better suggestion or needed to voice his or her concern. Sarah's thoughts raced for a moment or two, trying to think of another way to open the lock without the good old sonic screwdriver, but then all of that didn't matter any more as the Brigadier pressed down the door's handle, and it swung open almost by itself.
Surprised to find that it had not been locked to begin with, the four of them peeked warily into the warehouse beyond. There wasn't much to see from where they stood, except the empty, yet well-lit inside of the hall. "It appears that we are being expected...", the Doctor said while exchanging serious, mildly worried glances with his friends.
"Really? How could they know that we were coming?", Harry demanded to know, obviously more than mildly worried about that discovery.
"...Could it be that there is a mole working at UNIT?" Knowing that this assumption could be taken as an insult, Sarah posed her question hesitantly, although she knew that it had happened before. And within the last hours, only UNIT and the three of them had been involved, which made her theory even more likely.
Even so, the Brigadier shot her a half-furious glare. "That is preposterous, Miss Smith! We've taken great care to employ only those whom we can fully trust."
"If it has happened to Mike Yates – who was one of your best men – it can happen to anyone.", argued Sarah.
"We have taken even greater care after Captain Yates' treason.", he insisted.
"Or...", the Doctor suddenly cut in, "… there is a much simpler explanation. Whatever is in there could be guarding itself so well that there is no need for security measures."
"So, essentially, you're suggesting that they're overconfident...?" Doubtful, Harry raised an eyebrow.
"Now, we won't know unless we see for ourselves, will we?" After he had spoken this purely rhetorical question, the Doctor decided for himself to make the first step. Without as much as an announcement about what he planned to do he strode into the large hall, calling out loudly: "HELLO! Is Anyone home?" His booming voice echoed on the far walls and was thrown back to them several times. Sarah shuddered as the mostly empty hall with its high ceiling was filled with his presence.
Fearful that he might draw too much attention to himself, his assistant hurried after him. "Doctor!", she hissed as he stopped to wait for a response halfway across the width of the hall. If there was a trap ready to spring he had probably placed himself right in the middle of it and now he was excitedly waiting for something to happen. She caught up with him until she was back at his side, so that, if something happened, at least it wouldn't happen just to him.
A little perplexed by the interruption, he turned towards her. "Hm? What is it?"
"Don't do that…!", Sarah asked of him sternly, shaking her head.
The Doctor blinked at her surprised. "Oh, sorry.", he apologized briefly and shrugged while he attempted to explain himself. "I thought it might be good if we introduced ourselves first…?"
During the few seconds in which Sarah clarified the matter, Harry and the Brigadier had followed them inside. And so, as they all turned to look at the heart of the warehouse, they were met with the sight of a mirror labyrinth unlike any other. In the centre of the building was a stand, on top of which laid an ochre coloured tetrahedron. Harry and Sarah had seen several like this before, but always in the reflection of a mirror. This one was different in the way that it was the real one – and the only real one, as well. Around the stand, corridors of mirrors were arranged in a star burst pattern, similar to how Paris' main roads were arranged around the Arc de Triomphe. Each mirror was propped up on a support frame and adjusted very precisely so that it would reflect the image of at least one other mirror to the opposite of it. Even though they were all of different shape or size and came in a variety of frames, every one of the corridors created a perfect chain of mirrors which were reflecting the tetrahedron into each other.
"Oh, I say!", exclaimed Harry.
"I was right. It is a self-defending system.", the Doctor pointed out to them. "You've told me that every mirror with a tetrahedron in it can potentially absorb a human and produce a copy, is that correct?" Although he asked, he did not wait for someone to answer. "So, if the original, the real tetrahedron is the key, then the only way to disarm the mirrors is to walk down one of these corridors."
"That's almost impossible.", figured UNIT's medical officer. "Even if we ran down the corridor, it's so narrow that something will have yanked us in before we get to the middle. And believe me, I've been there, these reflections are pretty strong."
The Brigadier was thinking differently about the problem at hand. "It's far from impossible, Sullivan. I don't see a single living soul in sight. I could call in the RAF and have this place flattened by the hour without anyone risking their life in the process."
"I'm afraid that is not as much of an option as you think, Brigadier." The Doctor cut into the conversation while he was still examining the corridors from afar. "Not while we still haven't answered the question to where all the victims have gone."
"You are not seriously suggesting that each of these mirrors holds a victim...?"
Unwilling to allow himself to be criticised by the Brigadier's sceptical glance in return, the Doctor stepped closer to him to use his towering height for underlining his point. From one second to the next he had turned slightly upset. "Yes, I suggest that each of these mirrors contains possibly, not necessarily, a pocket dimension to imprison one or several people. If only one of the mirrors is shattered by accident, its pocket dimension will be lost for good, along with whatever is inside of it." He turned his head to look sideways at Lethbrigde-Stewart out of a haunting stare. "Could you rest easy at night not knowing how many people's lives you have destroyed?"
"I understand very well what you are saying, Doctor, and I don't plan on destroying any lives, as you should know.", answered the Brigadier. His voice was as emotionless as always, yet he averted his look. Obviously, he was unable to withstand the Doctor's strange glare for long, and so he was seeking the eye contact with one of the companions instead. "...Does anyone have another idea?"
The Doctor, too, turned towards his companions in expectation.
"Uhm...", stammered Harry, who was clearly lacking an idea to propose, and so the expectant look wandered over to Sarah.
For some reason, the first thing she could think of was the action UNIT had taken after Benton's disappearance. They had disabled the mirror by putting it into a crate. "We could… throw big blankets over the mirrors, so there won't be a reflection?", Sarah suggested hesitantly.
"It's possible, although it would take some time to organize enough blankets..." The Brigadier crossed his arms as he pondered about her idea. However, he was not exactly excited about it.
The Doctor's face, in contrast, lit up. "I've just had an even better thought!", he suddenly claimed and began to pace around the other three until he was standing right between Sarah and Harry. "Tell me, what is a reflection made of?"
"Glass and silver…?", guessed the medical officer, but his half-alien friend shook his head.
"No, that's a mirror, Harry. I'm talking about the reflection. The things we see. Maybe that's how I should ask: What enables us to see?" Despite the general lack of an answer, he was waiting for someone to reply something.
"Maybe you would just cut to the point, Doctor...", the Brigadier, who was getting very impatient about this little game, asked of him.
"Light!" The Doctor gave the word a slightly special pronunciation as he answered his own question. "Without light, the mirrors cannot see us. It's reasonably dark outside, and the light switches are right there-" He pointed at a set of switches near the entrance.
"But Doctor", Sarah looked up at him with a frown of worry on her face. "Without the light, we won't see anything, either."
"I could ask my men to bring their night vision gear.", proposed the Brigadier, but was stopped by the Doctor again before he was able to take action.
"No, leave the special equipment out.", he demanded, "They have their own sources of light. Weak ones, yes, but they might still be enough to trigger the mirrors' artificial sentience." In his attempt to calm the nerves of his companions, the Doctor glanced into each of their faces while he explained. "But it will be fine, you'll see. All we have to do is to walk in a straight line from here into the centre of the corridors and take the tetrahedron." With squinted eyes he attempted to estimate the distance between the start of the corridor and the middle of the warehouse. "What is that, only 40 or 50 yards away?" He smiled teasingly at the two military men. "Why, I could do it blindfolded!"
The Brigadier shot him an annoyed glance before he nodded approvingly. "All right, Doctor. We will give your idea a try."
"Great!" Pleased to hear the response, the Doctor's smile grew a little wider. "Then, would you kindly stay behind to operate the light switch, Brigadier? We will call to you once we're clear, so you can switch it back on." Although he looked at the Brigadier, he walked a few steps backwards in the direction of the corridor's entrance. "But make no mistake! If we are caught standing in the middle of the corridor, we will be easy pickings." Before he turned around, he exchanged a few glances with his companions, just to make sure that they, too, approved of his plan, since he was about to drag them into it.
Sarah had no objections, and neither did Harry, although they were not what one would call 'happy 'about it.
"Don't worry, I trust your judgement of the situation.", Lethbridge-Stewart reassured them.
While mentally preparing for the task they were about to face, the trio of heroes positioned themselves in front of the nearest mirror corridor. The whole of the situation made Sarah nervous, but she intended not to let it show. As her gaze wandered over to Harry to her right, she noticed that he was most likely feeling the same, and that he was not as good at hiding it as he probably thought he was. It was the frown on his face which gave his true emotions away.
"Are you scared of the dark?", Sarah asked him teasingly. Not to make fun of him, but to encourage him to prove her wrong.
"Me? No, not of the dark.", Harry answered, then chuckled nervously. "The mirrors, however, now that's a different story..."
The Doctor had overheard their conversation, and decided to join before the two of them could begin to count up all the reasons why they should be worried. "They won't harm us while we can't see our reflections. Try to think of that, Harry." Although he had addressed the medical officer, he showed both of them a toothy grin.
Sarah was smiling back almost instinctively, and could feel the optimism oozing out of his words. There was a certain confidence about being back together, the three of them, in the midst of danger, like old times. Not a fleeting thought of fear could darken her mood now.
That was, until the Doctor exchanged a decisive nod with the Brigadier, and the world turned black.