I stood in front of a perspex-covered picture, letting my eyes blur until it was just a mess of black and white, with my reflection behind it looking back at me. Dad was somewhere over the other side of the room. He'd moaned about the weather while we were waiting for the bus, but ever since we got to the museum he'd hovered at my shoulder silently, not meeting my eyes when I looked at him. Now he wasn't even doing that. I glanced over, and he was staring blankly at a display case. He'd been the one to suggest the special exhibition, but he looked like he was hating every moment. I felt my throat tighten. Three more days and then he'd go back to Sydney, and he hadn't even said he was glad to see me.

He sauntered over. 'Enjoying yourself, mate?'

I looked round, then back at the poster, willing my voice to stay steady. 'It's OK.'

'You know who he was, right?'

I didn't know what he was talking about. Then I followed his gaze to the photo and the plaque next to it. H. J. Martin was seconded to the Arab Intelligence Bureau. I said, 'Yeah, wasn't he that guy who got seconded to the Arab Intelligence Bureau in Cairo in 1914, where he swiftly made both enemies and staunch allies?'

Granddad would have laughed, but my dad just said, 'Yeah. That's the one,' without even letting on that he realised I was reading it off the wall.

'Including Morgan Astley, of course,' I said, in my best smarmy-private-schoolboy voice, 'who later wrote the introduction to The Owl of the Desert.' I pointed at the photo and added, 'Second from left.' But he still didn't get it.

He glanced at me. 'You're a bit of an expert, aren't you?' There was a gleam of something like malice in his eyes. 'Bet your grandfather loves that.'

'What?'

'Your grandfather. I bet he thinks it's great, you knowing all about H. J. Martin. Reminds him of me, maybe.'

'I ' I stared at him. It was weird, the way he said your grandfather, not my father. And there was a triumphant, aggressive sort of note in his voice, like he'd won a fight. I said, 'I don't know anything about him, really, I was only it's on the plaque.'

A second's silence. Then he laughed, but it was like I'd let him down. 'Oh. Right. Clever.'

I put my hands in my pockets and dug the toe of my trainer into the floor. 'Why wouldn't Granddad want me to know?' I said. 'I mean, he's a historian. He really likes it when I know things.'

'No reason,' he said. 'Got a bit of a thing about H. J. Martin, that's all. He Martin was a hero of mine when I was your age, and your grandfather . . .'

It didn't sound like he'd finished his sentence, but he didn't say anything else. I looked up at him, feeling lost. Who cared about H. J. Martin? I just wanted Dad to care about me. I heard his voice again reminds him of me, maybe and wished I'd pretended I did know about Martin.

'Old hypocrite,' Dad said, suddenly. There was a hard, venomous edge to his voice that made me feel cold and lost, as if he'd forgotten who I was. 'Get's so uptight about a bit of hero worship, and all the time he's living off the inheritance, living off the same bloody money that ' He cut himself off, staring at a picture on the far wall. 'And Tyme's End is sitting there, just '

I had no idea what he was talking about. I wanted to reach for his hand or touch his arm, just to remind him I was there but I didn't. I waited.

And after a long moment, Dad seemed to relax. He looked down at me, and his expression was smoother, more neutral. But there was still a strange emphasis in his voice, as if he was giving me the clue to a puzzle. 'He knew him, you know,' he said. 'Your grandfather knew Martin. He's probably in some of the pictures.'

'He knew loads of people,' I said. 'People are always coming round to interview him. Granddad knew Churchill.'

I'd got it wrong. Whatever Dad wanted, I hadn't done it. His expression changed, hardening. 'Jesus. He's got you thinking the sun shines out of his arse, hasn't he?'

'No I only meant '

'Forget it.' He turned away. 'Just don't kid yourself he's perfect, OK?'

I opened my mouth but my nose was prickling and I didn't trust my voice. I thought, I know Granddad's not perfect. If he was perfect, you'd never have had to go away. You'd never have left me behind. But I couldn't say it.

I moved sideways, pushing blindly through a knot of people, until I was looking at another photograph, trying to swallow the lump in my throat.

After a while he came and stood next to me. 'You finished?'

'Yeah.' I wished, too late, that I'd said no.

'Fine. Me too. Let's go.' He put his hand on my shoulder and steered me through the last room, walking quickly so I didn't even have time to glance at the display cases. His fingers dug into the tendons over my collarbone.

'If Granddad ' I said. 'Would he mind you bringing me here? I mean, what you said, about it reminding him of you do you want me, you know, not to mention it? I don't mind. I don't have to tell him. I can say we went to the Natural History Museum if you want. We went there with school, so I can lie '

He stopped walking suddenly, so I lurched into him. It was almost like he'd put his arm round me. I felt my face going red.

There was a pause. I heard a little sticky sort of sound as Dad opened his mouth. He said, 'No. No, Olly, you don't have to lie for my sake.'

'I don't mind I mean, I can keep a secret '

'No.' He smiled at me. 'Your granddad won't be angry with you. And you're my son. Why shouldn't I take you wherever you want to go?'

My cheeks blazed again. You're my son. It was the first nice thing he'd said to me.

'Come on, Olly,' he said, and went down the steps ahead of me, clicking his fingers behind his back to make me follow. 'You've been a good lad today. Didn't complain about the rain or anything. I want to buy you a present.'

'But ' But you can't even afford the Tube, I wanted to say. I don't want a present. I'm fine. All I want is for you to come and live in London. But he was already striding round the corner, into the gift shop. He glanced round, then made a beeline for the table in front of him. There were piles of books, all with a black-and-white photo on the front, the same photo that I'd been staring at before. I stood and watched as he picked one up, turned it over to check the price, and then took it to the till.

I said, 'Um . . . I'd rather have ' and stopped, because it didn't matter. He was buying me a present. I didn't care what it was. Even if it was a big adult book about someone I'd never heard of before today.

The woman at the till gave Dad his change and put the book into a plastic bag. He smiled over his shoulder and held it out to me with one hand, putting his wallet away with the other. I smiled back and took it from him, tilting the bag so I could see the front cover. H. J. Martin: A Biography. It was huge. It looked serious and thoughtful, the kind of book Granddad wrote. The face in the picture was already familiar, like someone I'd known when I was too small to remember. But I couldn't imagine ever actually reading it. I said, 'Great. Thanks.'

'You could sound a bit grateful.'

'I am. Honestly. Thanks. I'll try to it looks good.'

'It ought to impress your granddad anyway,' Dad said. He had a gleam of enjoyment in his eyes, and I told myself it was because he liked giving me something. 'I'd've loved it, at your age.'

I squeezed my tongue against my teeth and swung the plastic bag from my fingers. In that case I'll read it, I thought. It was funny though, because Dad didn't seem like someone who liked books at all. He didn't even have a proper job. And Granddad talked to him like he was stupid.

'I'd better take you home.'

'OK,' I said. I swung the bag hard against my leg, so that the corner of the book bashed into my knee. That was it for today, then. And then there was tomorrow, and Friday and Saturday, and then he was flying back to Sydney.

He didn't say anything, even while we were waiting for the bus. I watched the rain spatter against the sides of the bus shelter and tried not to feel miserable. He'd bought me a book. That was good, wasn't it? He liked me enough to buy me a book. And when we got on the bus he gave me the seat next to the window and leant over me to rub the condensation off the glass. I sat very still and breathed carefully, hoping he'd put his arm round me. But he didn't.

The front door was double-locked, which meant that Granddad wasn't in. My dad was already going back down the steps, his hand raised in a kind of wave. I ran halfway down to catch up with him and managed to stop myself before I grabbed his arm. 'Do you want to Granddad's not here. Do you want to come in? I'll make you a cup of tea or something. Please?'

He turned round and looked at me, grimacing. 'I'd better not, Olly. See you tomorrow, OK?'

'But he's not here,' I said. 'Are you hungry? We've got crisps and things. Rosina went shopping yesterday.'

'Thanks, son, but I'd better scarper. Really.'

'Please. Just for a bit. If Granddad comes back I'll say I invited you.'

'Well . . .' He tugged at his nose, staring at me like I was a maths question he was trying to solve. 'Not for long, OK? Just a quick cuppa. Then I'd better go.'

'Yeah, 'course,' I said, trying to sound cool. 'That's fine.'

It was funny though. Making tea and getting the biscuit tin out and trying to find the crisps, and all the time thinking, I'm making tea for my dad, I'm getting biscuits out for my dad. I felt all warm and floppy. He did like me. He wouldn't be here unless he liked me. I dug around in the cupboard looking for the sea salt and balsamic vinegar crisps that Rosina bought and took it all up to the drawing room on a tray. He grinned when he saw me. 'Bloody hell, Olly, you've got enough food to float a battleship.'

'I'm hungry.' But I wasn't. I watched him pour the tea he took three sugars and it was like the drawing room was glowing.

He glanced up and saw me looking at him. For a moment I thought he was going to say something like, I'm not a bloody circus, mate, but then he blinked and gave me a sort of uncertain smile. He picked up his tea, holding the cup in both hands like it was a mug, and tilted his head towards the bag on the sofa. 'You left your book downstairs. I brought it up for you.'

'Thanks.' I picked it up and slid the book out. It still didn't look like the sort of thing I'd ever read, but . . . 'Thank you.' I put it down on the arm of my chair.

I heard the front door squeak and bang and click, the way it always did. My dad heard it too; he stopped before the teacup got to his mouth and said, 'Is that ?'

'Don't worry, it's probably Rosina.' But it wasn't Rosina's day. My heart was banging. It was Granddad. He'd popped out for cigarettes or matches or something and now he was back and he'd know I was in because of the front door not being double-locked and he might come to say hello and then he'd see My dad half-rose to his feet; then he sat down again. 'It's your grandfather, isn't it?'

'I dunno. But, look, it's not your fault you're here, I made you '

'You didn't make me do anything, mate.' He squared his shoulders, like Granddad was already there in front of him, threatening to call the police. 'Who does he think he is, anyway? How am I supposed to get to know you properly if I can't even come into the house? It's ridiculous.'

'How could you possibly get to know him properly in a week? An equally ridiculous suggestion, I'd say.'

Granddad. He was there in the doorway, peeling the plastic film off a packet of cigarettes.

I said, 'Granddad, he was only having a cup of tea, and I asked him, because you weren't in, and we were hungry, and '

'Thank you, Olly.' He held up a hand to stop me. 'Please, sit down, both of you.' He came into the room and put a hand on the teapot, checking how hot it was. 'May I?' He didn't wait for me to answer, just poured some tea into the cup I'd brought up for myself. He was casual and deliberate at the same time, like he was doing it on purpose. He stirred it and tapped the spoon on the edge of the saucer. 'Philip, I thought I made my preferences on this point perfectly clear. You're not welcome in this house.'

My dad's face did something strange. He said, 'Look, I'm only here because come on, Father '

Granddad turned to me. 'Olly, did you pour your father's tea? There appear to be tea leaves floating in it.' There was an edge to his voice; someone was in big trouble. I just didn't know if it was me.

'I don't know,' I said.

'Well, perhaps you should '

He stopped, because he'd caught sight of the book on the arm of my chair. It was almost a double take; it would have been funny except for the look on his face. Like I didn't know what it was like. Like meeting your worst enemy in heaven. Like seeing a ghost.

'Whose is that?' He raised his hand and pointed with the spoon. It should have been funny. But it wasn't, somehow.

'Mine,' I said, scared to speak but more scared of not answering him. 'Dad gave it to me.'

He lowered the spoon, very, very slowly. 'Did he,' he said, but it wasn't a question. 'Give it to me, please, Oliver.'

I picked it up and held it out for him to take. He reached out But I didn't let him take it. I snatched it away, just as his fingers touched it, before his grip could tighten. I jumped back, my heart pounding, and ducked out of his way, but I couldn't hold on to the book. It dropped on to the floor. Granddad's cup of tea fell and smashed next to it, splattering tea all over the cover.

For a moment we stared at each other. His face looked bleak, foreign. I didn't recognise it.

My dad said, 'It's none of your business. He's my son.'

Granddad's gaze faltered and he glanced down at the wreckage on the floor, but when he looked back his face was his own again. 'Go to your room, Olly. I need to speak to your father alone.'

I looked down at the book, and then at him. 'But '

'Go to your room.'

I went. Granddad stood in the doorway of the drawing room, watched me go up the stairs to my room, and shut the door with a sharp, decisive click. I stood on the landing, counted to twenty, and then crept back down to sit on the lowest step, my arms wrapped round my knees. I felt sick and cold. My stomach was sinking slowly, like a battleship.

At first their voices weren't loud enough for me to hear what they were saying. I leant forward, watching the shadow under the door. Then I heard my dad say, 'For God's sake, it's just a book!'

The shadow moved suddenly, as if Granddad had walked towards him, away from the door. He replied quietly, precisely, so all I could hear was the rumble of his voice and the consonants.

Dad said, loudly, 'I thought Olly would like it, that's all! Jesus, you are so arrogant. This is about me and my son. Why the hell would it be about you?'

I felt a little flash of warmth because of the way he'd said my son, but it died immediately, leaving me colder than ever. My face felt funny, like the skin was sticking to my skull.

Granddad said something else, indistinctly, in that low, dispassionate tone.

'Well, what if I do? You've got him wrapped round your little finger he bloody worships you! Do you have any idea how hard this is for me? I've come all this way, and all I find is that he's a spoilt little brat who thinks you're the bee's knees because you buy him everything he wants '

And then the noise of something breaking. My dad must have broken something, because Granddad wouldn't I'd never seen him break anything, even by accident. I could feel the tears building up again in my throat, inexorably, like when you put your thumb over a dripping tap.

I heard Granddad's voice again, still quiet, but suddenly so clear it was as if he knew I was there and wanted me to hear. 'Don't you dare call Oliver a spoilt brat!'

Then, unbelievably, there were two voices shouting at once, blurring, wiping each other out so I couldn't hear the words. I'd never heard Granddad shout, not in thirteen years. His voice rose above Dad's, making my teeth vibrate.

'You know nothing whatsoever about him! You reckless, selfish, predatory idiot you come over here and think you can play at being his father. You appal me. It's contemptible. Who do you think you are? Have you even noticed how upset he is? Or did you imagine that it was perfectly normal for him to be constantly on the edge of tears? He was fine before you got here. It would have been better if you'd never come. Have you any conception at all of the damage you've done? If you had any decency you'd leave him alone '

And it went on. On and on and on, a tight, furious, wounded voice I'd never heard Granddad use before, telling my father I'd be better off without him. I wanted to go down and shout at him to shut up. I wanted to say, I don't care if he does damage me, I'd still rather he was here, I'd still rather . . . He's my dad.

'And I cannot express my Philip, you bought him that book because you knew how I'd react. You let the boy think you wanted to buy him a gift, when you were simply using him to get at me. You haven't changed, have you? It's despicable. I suppose you still think that somehow I am responsible for what you '

'Don't lecture me, you pompous bastard! As if you knew anything about being a decent father as if you cared what I did, as if you'd ever '

'All right. I don't propose to discuss the past. I am only, and absolutely, concerned with Oliver. And I will not let you do this to him.'

'Oh, yeah, of course, you want to turn him against me '

'I hardly think I need to bother. Oliver is quite intelligent enough to understand the situation.'

Silence.

Then my father's voice again, only this time it was low and sibilant, spitting the consonants, and for the first time he sounded like Granddad. It made my back feel shivery, like I had a temperature.

He said, 'All right. You want to keep on punishing me. You want to keep me away from my son. You win.'

I opened my mouth. There was a tiny noise, barely audible, as my vocal cords opened and closed. No. He'd go away and never come back, and he was my dad . . .

The drawing-room door opened and Dad was standing there, his face blotched and red over the cheekbones. He stared at me, and his mouth moved, but he didn't say anything. I looked at him, scared that he could see how I felt, but glad too, because if he could see how I felt he might not leave.