'Sonic screwdriver, please,' requested the white haired form of the third Doctor as he buried his head within a large metal canister, one hand tinkering around with the controls inside, the other stretched out to receive the instrument.
'Here,' said Jo, handing the device over, wearily. He took it without looking round, and continued to work away quite happily. 'It might help,' said Jo, scathingly, 'If I knew what you were trying to do in there.'
'Oh, I doubt it,' replied the Doctor, off-handed. 'It's not exactly easy for a human mind to take in the concepts of temporal engineering.'
'I take it you're trying to get the TARDIS to work again,' commented Jo, as she walked over to her companions craft, stood in its usual position in the corner of the lab.
To her surprise, the Doctor suddenly stepped away from the canister and turned to face her, beaming. 'Right. Again, Jo!', he announced happily. He closed the box and picked up two wires which protruded from a hole in the back, then set off towards his grounded machine, indicating that his companion should follow, She did, and found herself in the TARDIS' impossibly large control room.
The Doctor was already at the far side of the central console, where he had removed one of its panels and was proceeding to fiddle about inside. The two wires from the Doctor's canister trailed across the floor to where he was working, and Jo was careful to avoid stepping on them as she moved round the console to see what her companion was up to. As she had expected, she didn't understand any of it, but even as she sighed in despair, the Doctor jumped to his feet and began to activate a variety of switches on the console.
'What are you doing?' she cried in alarm.
'We're taking a little trip,' came the calm reply.
'A trip?' cried Jo, wondering fearfully what the far side of the Universe was like.
'Oh, just across the lab, don't worry,' the Doctor assured her. 'I just want to see if my new box of tricks is any good.' He completed his programming with a flourish and stepped back from the console with an expression of satisfaction that changed instantly to horror as suddenly, a large portion of the console blew up in his face.
Jo giggled as the Doctor stared incredulously at the steaming controls. 'Perhaps you should have expected that by now?' she teased. The Doctor shot her a withering glance and pulling the two connecting wires from the console, he strode briskly out of the TARDIS.
'Another failure,' he growled, ripping the two wires viciously from the back of his metal canister, and flinging them angrily to one side.
'Isn't it worth another try?' Jo asked, feeling rather sorry for him.
The Doctor shrugged. 'Perhaps,' he replied. 'Not yet thou. I think I've had enough for one--' He was cut short as suddenly, a strange, yet familiar noise echoed through the lab - a wheezing, groaning sound which the Doctor and Jo both recognised as that which accompanied the dematerialisation of the TARDIS. As one, they turned to the craft - but the noise was not coming from that.
'It's the box!' cried Jo, as realisation dawned upon her. It was still in its position on the lab bench, but now it had begun to glow - dimly at first, then brighter and brighter, until they could no-longer bear to look at it directly. It was this scene that greeted Brigadier Alistair Gordon Lethbridge-Stewart, as he rushed into the room and demanded to know what was going on. The raucous groaning sound had reached fever pitch now, drowning out his yell, drowning out everything in an ear-splitting cacophony...
And then suddenly, there was silence.
The canister was glowing no longer, and showed no signs of its earlier activity - and the lab's three occupants were just staring at it, deafened by the sudden silence.
'What on Earth is going on here?' the Brigadier demanded to know, breaking the silence in a quiet but agitated voice.
The Doctor was already moving slowly towards the canister, one hand up to indicate that neither of them should follow him. 'If you'll just bear with me for a moment, Brigadier,' he muttered, 'that's just what we're about to find out.'
He flipped open the lid.
Jo screamed, the Brigadier jumped and the Doctor stepped back in surprise as a stream of glowing crystals swept suddenly out of the box, and hovered in mid-air before them, pulsing irregularly.
'What are they?' Jo hissed, awe-struck, but the Doctor merely shrugged, eyes staring intently at this strange phenomenon.
Slowly, very slowly, the particles were fading, dissolving into the air itself, until they were gone, leaving no sign that they had ever been there - apart from the three humanoids who stood in the UNIT laboratory, bewildered by what they had just seen, and simply staring at where they had once been.
The Doctor was the first to move. walking slowly towards the still open box and lifting it easily in one hand. 'Empty!' he announced.
'Empty?' Jo echoed. 'But what about your machine thing?'
'I'm not entirely sure,' her companion replied slowly, weighing the metal canister thoughtfully in his hand, 'but I intend to find out.'
The next morning found Jo Grant alone in the Doctor's lab, soldering some wires inside a complex-looking helmet-like device. She was interrupted in her work by the sudden arrival of the Brigadier, the morning paper tucked under his arm.
'Where is he?' he asked briskly, glancing around the room.
'In there,' Jo told him, nodding towards the TARDIS.
As the Brigadier eyed the Doctor's craft suspiciously, the Time Lord suddenly hurried out, a large cuboid piece of machinery cradled in his arms. He walked swiftly across the lab and deposited it on the bench next to Jo, apparently unaware of the Brigadier's presence. 'How are you doing? He asked her.
'Nearly finished,' Jo grunted, straining to get at something within the device.
The Brigadier cleared his throat loudly, and the Doctor turned to face him. 'Ah, good morning, Brigadier,' he said cheerfully, 'Any news?'
'Well, as a matter of fact...' the Brigadier began, but before he could get any further, the Doctor snatched the newspaper from him and began to read the front page.
'Oh dear,' he muttered, 'that's not very good, is it? In fact, it's extremely dangerous!' He flung the paper down on the bench, and turned to face his friends solemnly. 'I'm afraid,' he announced, 'that your planet is in the most terrible danger.'
'What do you mean?' cried the Brigadier.
The Doctor grabbed the newspaper once more, and thrust it into Jo's hands. 'All over the country!' he exclaimed.
'Sightings of what exactly?'
'The Cosmic Dust.'
'The Cosmic Dust?'
'That's right!' The Doctor grabbed an atlas from the shelf and flicked through it until he found a detailed map of England. He placed it on the bench and Jo and the Brigadier gathered around to see what he was getting at.
The Doctor picked up the paper again and, referring to the article as he went along he began to make a number of pen marks on the map. 'Now, this is where we are,' he explained, pointing to one of them, 'and this "cosmic dust" as you call it has been sighted here...and here...and here...and here!'
'Almost in a straight line.' Jo observed.
'Exactly!' the Doctor exclaimed, with some satisfaction.
'So you think it's actually going somewhere?' asked the Brigadier, incredulously.
'It certainly looks like it,' the Doctor commented.
'But where?' asked Jo.
'Here perhaps?' the Doctor suggested, making another pen mark on the map.
The Brigadier was shocked. 'The nuclear weapons plant?' he exclaimed, gaping at the map, the line of pen marks and the inescapable conclusion that the Doctor had come to. 'But it would wreak havoc if it got into that!'
The Doctor nodded glumly. 'That's probably the idea!'
'But what can we do?' stammered the Brigadier, aware of the fact that he had never felt so helpless in his life.
'Good question,' remarked the Doctor. He turned to his assistant. 'Jo, have you finished that soldering job yet?'
'Yes, here you are.' said Jo, handing him the helmet she had been working on.
'And what on Earth is that supposed to be?' the Brigadier wanted to know.
'Well,' the Doctor explained, 'working from the fact that this cosmic dust was able to use the TARDIS to apparently change places with my machinery in the box, I've managed to work out quite a lot about their molecular structure, enabling me to build this!' He indicated the helmet, proudly.
'So, what does it do?' the Brigadier asked impatiently.
'Well, with this,' the Doctor explained, popping the helmet onto his head, 'I should be able to communicate with our little friends.'
'Communicate with them?' roared the Brigadier. 'We should destroy them!'
The Doctor sighed and turned to the large cuboid machine he had brought from his TARDIS. 'I've built something to do that too,' he said, 'but I sincerely hope that it won't be necessary.'
'That's more like it,' the Brigadier said happily, 'A nice, straight forward solution to the problem.'
'Which we'll only use,' the Doctor said firmly, 'If everything else fails. Now, I suggest we get going.'