The next morning, Susan woke up to find a donkey in her living room.

It did not seem particularly unhappy, although it had eaten the contents of both of her vases of flowers, spilling water on the carpet and leaving shards of pottery everywhere. She gasped in surprise; its only response was to stare back at her with sad brown eyes.

Her life experience had not really equipped her to deal with livestock in her flat.

'Livestock? Or are you a beast of burden? I wonder if I would have learnt about this at school,' she said to the donkey, as she led it outside to her little garden, grateful that she lived on the ground floor.

'Oh dear,' she continued. 'Talking to myself. I think I am becoming hysterical.'

It didn't reply. She took this as a good sign.

Once it was outside and munching on a bowl of oats – what she would have made her porridge with, she thought, somewhat resentfully – she called the RSPCA. To her surprise, the phone was answered almost immediately by a cheerful lady with a Yorkshire accent.

'Um, hello. I don't quite know how to say this, but I woke up this morning and found a donkey in my home,' said Susan, trying hard not to sound mad.

'That must've been a surprise for you!', came the reply.

'It was rather. What do you suppose I should do?'

'It'll have escaped from somewhere. We just need to find out where and get them to come and pick it up. Whereabouts do you live?'

'South Finchley. In North London.'

'Ah, OK. It's probably from the zoo in Golders Hill Park, then.'

The zoo was not that close to her house, actually, and it seemed unlikely that the animal had walked from there; but she decided that getting rid of the donkey was more important than being right about its origin. The zoo could sort it out.

'What do you suppose I should do, then?', she asked.

'Well, I can give 'em a call. They'll be round this afternoon, I imagine. What's your address?'

Susan told her; but then realised she had promised to meat Iris Lafey at ten.

'I need to be out for something this morning, rather urgent, I'm afraid. If I left the key somewhere, would that be all right?'

'Can't see why not. If it was easy for the donkey to get in, it should be easy for it to get out!'

Susan closed her eyes. She must have left the door unlocked last night, mustn't she? Had it been open? She was grateful that the only thing she had found was a donkey.

She gave the RSPCA lady her details, left the donkey some water, and set off to the Heath.

It was an hour's walk from her flat to the Heath, but Susan decided she needed the exercise, and to blow away some of the stress of the donkey incident; and anyway, any sort of transport at this time on a Sunday morning would be slow and miserable. So she set off with an umbrella, and strode through the drizzle and the suburbs.

She had always loved the Heath. George and she had spent many happy afternoons there walking and talking. She remembered reading the bizarre ancient bye-laws with him and laughing about the rules that made it illegal to mend chairs; she remembered holding hands in the sun...

She walked more quickly.

Even on a grey Sunday morning, there were people out. Dog walkers, joggers, tourists, bird watchers... London wasn't a city that never slept, but it was definitely a city that knew how to do a civilised lazy morning. It was why she had agreed to meet Lafey here; she hoped the passers-by would offer some sort of protection.

Lafey was there already, pacing up and down the path. She was wearing the same embroidered dress, brilliantly red like a bead of fresh blood, somehow even brighter than the jogger's neon sweatbands. She walked like a hunter or a dancer, controlled but carrying the threat of explosive movement.

'Susan Pevensie!', she called.

'Good morning, Iris,' replied Susan, once she had reached her. 'Shall we sit here?'

Lafey scowled, but sat on the bench that Susan indicated. It had stopped raining, and was not cold, but it certainly wasn't the weather that Susan would have chosen to sit outside in. The wind gently nudged the trees and the leaves shivered; Kenwood House loomed to their left, pale and angular.

Lafey could not sit still. She twitched and fidgeted. She was silent for as long as she could manage, while Susan settled herself; and then she started speaking quickly, urgently.

'Susan Pevensie, I am glad you saw sense. You must help. There has been a terrible crisis...'

'Iris, please. If you can't get it right, please, just call me Susan.'

'What, Susan Pev...? I understand. I will call you that.'

'Thank you. Now what were you going to say?'

'Susan, there has been a terrible crisis. There are people coming to this world, people and things. They are coming here because they are lost. We think that you may be important because you are... you were... a Pevensie.'

Susan sighed. She found the intensity of the woman in red draining, as if she were playing some endless game which involved constant vigilance.

'Is one of those things a donkey?', she asked, trying to retain some joviality.

Iris narrowed her eyes and leaned forward. 'Perhaps,' she hissed. 'You must be very wary of it. It might be dangerous. It might be full of rage. But, what, Susan...? What is a "donkey"?'

'Iris, I think it's just a coincidence.'

'There are no such thing as coincidences, Susan.'

That was actually the first thing that Lafey had said that made a degree of sense to her. But she certainly hadn't sensed any danger or rage from the donkey. I suppose I wouldn't think that if I was an oat, she thought. It ate them quickly enough. Oh, this is ridiculous.

'No, you'e probably right. But I'm sure the lion will turn up and sort out. That's what he did. It wasn't really worth us doing anything at all, looking back at it: Aslan was the only thing that actually changed anything in Narnia. Oh, that and Edmund eating Turkish delight. The rest of us all felt jolly important at the time, but the reality? We didn't do anything useful! So I'm just going to look after my new dangerous donkey, and wait for Aslan to turn up and do his job.'

'Aslan has gone, child.'

'Oh, they always said that. He just likes making a dramatic entrance. Or he's one of these people that's always late for everything.'

Lafey suddenly looked up, her eyes darting at the trees. She grasped the arm of the bench, her fingers shivering as she squeezed the wood.

'What's the matter, Iris?', asked Susan.

'Can't you hear it?'

Susan listened; the trees were rustling their leaves and the branches swayed slowly.

Lafey stood, looked down Parliament Hill, into the grey that was London on a dreary summer morning.

'I can just hear the trees moving in the wind. Please, sit back down.'

Lafey looked down at her, her wild eyes drilling into Susan's mind.

'There's no wind, girl,' she hissed.

Susan slowly stood too. She looked at what Iris was looking at, at the other trees dotted across the heath, all completely still; and she glanced up, and saw how the trees around them were swaying as if in a high gale. She shivered in fear.

'Iris, I think I would like to walk to Kenwood House now. Would you come with me?'

But Lafey was already away, stalking towards the end of the avenue. Susan hurried to catch her up. As she walked, she could hear whispers in the rustling; they sounded sleepy, as if the trees were just waking, but what they were saying was clear to her Narnia sharpened ear.

'Help us, Susan...'

'We are lost...'

'We left the darkness....'

'Help us...'

Iris was waiting just beyond the avenue of trees, her face grim. Beech leaves fluttered down around her as Susan hurried out.

'Left the darkness...'

Susan didn't look back as she walked.

'Those are tree spirits,' she said. 'They were talking to me, asking for help. What did they mean about leaving the darkness?'

Lafey waited for Susan to catch up; but then she set off, striding down the Heath. Susan could just about keep up with her.

'Aslan left,' said Lafey. 'He ended that realm and moved everyone else in it to another place, and then sealed the way.'

'What do you mean?', asked Susan. 'Look here, Iris Lafey, or whatever your real name is; not that, I imagine. I have had quite enough of cryptic little comments. I insist you tell me what is going on, right now.'

Lafey slowed sharply. She looked around. They were walking on the Heath proper now, on scrubby grassland leading down the hill to the Wood Pond.

'It's more open here. We should be safer,' she said. 'Susan: you are wiser than you look. Iris Lafey is not my true name, but I use it for this realm. I will tell you the whole story. I was hoping to tell you somewhere more secure. But now we're here, and it will have to do. But I ask you this: we need to avoid trees, and water, and mountains, and the wilds. Anywhere that would draw the souls of Narnia. It's bad enough that those dryads are here; we mustn't suck any more things into this realm. We should find somewhere full of humans. The Old Narnians hate humans.'

'That's why you were in Camden, isn't it? It's heaving with people.'

'Again, you're correct. I may have misjudged you. So why did you pretend to be stupid? Why did you say that the lion would come?'

Susan shrugged. 'As I said: he always has before. Generally after other people have done the dirty work, though.'

Lafey suddenly stopped and spun to face her, struck with realisation. She flung her hands out and gestured wildly as she spoke.

'You weren't there, were you? I hadn't realised! And this is why: you stopped trusting him. You lost your faith, Susan. He never pulled you back that last time, never gave you the choice. That's why you don't know. It is much, much worse than I thought.'

Susan smiled, sadly. 'No. He never took me back. He told me and Peter that we could never return after the second time. He's many things, but he's not a liar. By the way, if you want to avoid water, it's going to be difficult if we keep going this way. We're walking towards the ponds. I think we should double back and go to my flat. We can avoid the dryads.'

'And yet Peter Pevensie returned.'

This time it was Susan's turn to be shocked.

'What? When? He never said, and they always told me about their trips when they got back.'

'You really don't know. I'll explain.'