Strangest of all were the incongruous objects dotted about here and there. They included a number of old-fashioned chairs and the statue of some kind of bird on top of a tall column. Beside it stood Susan, looking at them in utter amazement.

Ian blinked incredulously, his mind filled with a wrenching sense of unreality. He heard the old man say calmly, 'Close the door, Susan.'

Susan touched a control on the central console, and the door closed with an eerie electronic hum.

The old man took off his cloak and hat, and tossed them onto a chair. The clothes beneath were even more eccentric (check trousers with old-fashioned boots, and a kind of frock-coat worn with a cravat and a high-wing collar). The general effect was that of a family solicitor from some nineteenth-century novel. Like the statue and the padded chairs, the old man looked strangely out of place in this ultra-technological setting.

But he was obviously quite at home here. Rubbing his bony hands together, he looked disapprovingly at the two intruders. 'I believe these people are known to you, Susan?'

'They're two of my school teachers.' Susan seemed almost as astonished as Barbara and Ian. 'What are you doing here?'

'Presumably they followed you,' said the Doctor acidly. 'That ridiculous school! I knew something like this would happen if we stayed in one place too long.'

'But why should they follow me?'

'Ask them,' said the old man. He turned away to study a row of instruments on the central console.

Barbara looked around the astounding room, and then back at Susan. 'Is this place really your home, Susan?'

'Yes... well, at least, it's the only home I have now.'

The old man looked up. 'And what's wrong with it?'

Ian rubbed his eyes and blinked - but nothing changed. 'But it was just a police box.'

The old man smiled. 'To you, perhaps,' he said condescendingly.

Barbara said, 'And this is your grandfather?'

'Yes.'

Barbara turned to the old man. 'So you must be Doctor Foreman?'

The old man smiled. 'Not really. The name was on the notice-board, and I borrowed it. It might be best if you were to address me simply as Doctor.'

'Very well, then - Doctor. Why didn't you tell us who you were?'

'I don't discuss my private life with strangers,' said the Doctor haughtily.

Ian was still struggling to understand the central mystery. 'But it was just a police box! I walked all round it. Barbara, you saw me.

How come it's bigger on the inside than on the outside?'

'You don't deserve any explanations,' said the Doctor pettishly.

'You pushed your way in here, uninvited and unwelcome...'

'Now, just a minute,' said Ian doggedly. 'I know this is absurd.

It was just a police box, I walked all round it. I just don't understand...'

The Doctor was fiddling with one of the controls. 'Look at this, Susan,' he said querulously. 'It's stopped again. I've tried to repair it, but...' He broke off, shooting a malicious glance at Ian. 'No, of course, you don't understand. How could you?'

'But I want to understand,' shouted Ian.

The Doctor waved him away. 'Yes, yes... By the way, Susan, I managed to find a replacement for that portofilio. It was quite a job, but I think it'll serve...'

Ian pounded his fists against the walls of the room. 'It's an illusion, it must be.'

The Doctor sighed. 'What is he talking about now?'

'Ian, what are you doing?' whispered Barbara.

'I don't know,' said Ian helplessly.

The Doctor smiled maliciously at Ian's confusion. 'You don't understand, so you find excuses for yourself. Illusion, indeed! See here, young man. You say you can't fit a large space inside a small one? So you couldn't fit an enormous building into a little room?'

'No,' said Ian. 'No, you couldn't.'

'But you've invented television by now, haven't you?' said the Doctor.

'Yes.'

'So - by showing an enormous building on your television screen, you can do something you said was humanly impossible, can't you?'

'Well, yes, in a sense,' said Ian doubtfully. 'But all the same...'

The old man cackled triumphantly. 'Not quite clear, is it? I can see by your face that you're not certain, you don't understand. I knew you wouldn't. Never mind!' The Doctor seemed positively delighted by Ian's lack of comprehension. He fiddled with the control console, muttering to himself. 'Now, which switch was it? This one - no, this one.' He looked up at Ian and Barbara. 'The point is not so much whether you understand what has already happened to you, it's what's going to happen to you. You could tell everyone about the ship - and we can't have that.

'Ship?' asked Ian, more confused than ever.

'Yes, ship,' said the Doctor sharply. 'This thing doesn't roll along on wheels, you know.'

'You mean it moves?' asked Barbara.

Susan nodded proudly. 'The TARDIS can go anywhere in Time and Space.'

'TARDIS? I don't understand you, Susan.'

'Well, I made the name up, actually. TARDIS, from the initials. Time and Relative Dimension in Space. Don't you understand? The dimensions inside are different from those outside.'

Ian drew a deep breath. 'Just let me get this straight. A thing that looks like a police box standing in a junk yard... and it can travel in Time and Space?'

'Yes,' said Susan.

'Quite so,' confirmed the Doctor briskly.

'But that's ridiculous!'

Susan looked in anguish at the old man. 'Why won't they believe us?'

'Well, how can we?' said Barbara patiently. 'It's so obviously impossible.'

Susan stamped her foot in frustration, and the Doctor chuckled.

'Now, don't get exasperated, Susan. Remember the Red Indian when he saw his first steam train - his savage mind probably thought it was an illusion too!'

'You're treating us like savages,' said Ian bitterly. 'Savages or children!'

The Doctor gave his infuriatingly superior smile. 'Am I? The children of my civilisation would be insulted!'

' Your civilisation?'

'Yes, my civilisation. I tolerate this century, but I don't enjoy it.

Have you ever thought what it's like to be wanderers in the fourth dimension, young man? Have you? To be exiles! Susan and I are cut off from our own civilisation, without friends or protection, but one day we shall go back.' He stared into the distance. 'Yes, one day...

one day...'

Perhaps the human mind can only take in so many surprises at a time. At this new revelation, Barbara and Ian exchanged looks of sheer disbelief.

'It's true,' cried Susan desperately. 'It's all true! You don't know what you've done, coming here.' She turned to the Doctor.

'Grandfather, let them go now, please, they can't harm us. I know these people, their minds reject things they don't understand. They won't tell anyone and even if they did, they wouldn't be believed.'

The Doctor's face was suddenly cold and hard. 'No.'

'You can't keep us here!' said Ian defiantly.

'Can't I?' said the Doctor. Something about his confident smile made Ian feel very uneasy.

Barbara went over to Susan and put an arm around her shoulders. 'Susan, listen to me. Can't you see that all this is an illusion, a fantasy? If you like, it's a game that you and your grandfather are playing. You can't expect us to believe it as well.'

'But it's not a game,' said Susan desperately. 'It's not! I love England in the twentieth century. I love your school. The last five months have been the happiest of my life.'

'You talk as if you weren't one of us,' said Barbara. 'But you are! You look like us, you sound like us...'

Susan's face was solemn. 'I was born in another time, another world.'