ON SATURDAY MORNING JOCHEN and I went down to the Westgate shopping centre in Oxford – a shopping mall, of sorts, concrete, ugly but useful as most malls tend to be – to buy some new pyjamas for Jochen (as he was going to be spending a night with his grandmother) and to pay the penultimate hire-purchase instalment on the new cooker I'd bought in December. We parked the car in Broad Street and walked up Cornmarket, where the shops were just opening and, even though it promised to be yet another fine, hot sunny day, there seemed to be a brief sensation of freshness in the morning air – a tacit conspiracy or wishful illusion that such hot sunny days were not yet so commonplace as to have become tiresome and boring. The streets had been swept, the rubbish bins emptied and the sticky bus-and-tourist-clogged hell that was a Saturday Cornmarket in reality was still an hour or two away.

Jochen dragged me back to look at a toyshop window.

'Look at that, Mummy. It's amazing.'

He was pointing to some plastic space gun, encrusted with gimmicks and gizmos.

'Can I have that for my birthday?' he asked plaintively. 'For my birthday and next Christmas?'

'No. I've got you a lovely new encyclopaedia.'

'You're joking with me again,' he said, sternly. 'Don't joke like that.'

'You have to joke a little in life, darling,' I said, leading him on and turning down Queen Street. 'Otherwise what's the point?'

'It depends on the joke,' he said. 'Some jokes aren't funny.'

'All right, you can have your gun. I'll send the encyclopaedia to a little boy in Africa.'

'What little boy?'

'I'll find one. There'll be masses who'd love an encyclopaedia.'

'Look – there's Hamid.'

At the foot of Queen Street was a small square with an obelisk. Clearly designed to be a modest public space in the Edwardian part of the city, now, with the modern redevelopment, it served only as a kind of forecourt or ramp to the maw of the Westgate centre. Now glue-sniffing punks gathered at the steps around the monument (to some forgotten soldier killed in a colonial skirmish) and it was a favourite spot for marches and demonstrations to begin or end. The punks liked it, buskers liked it, beggars liked it, Hare Krishna groups tinkled their cymbals and chanted in it, Salvation Army bands played carols in it at Christmas. I had to admit that, nondescript though it was, it was possibly the liveliest and most eclectic public space in Oxford.

Today there was a small demonstration of Iranians – students and exiles, I supposed – a group of thirty or so assembled under banners that read 'Down with the Shah', 'Long Live the Iranian Revolution'. Two bearded men were trying to encourage passers-by to sign a petition and a girl in a headscarf was listing, in a shrill singsong voice, the Pahlavi family's iniquities through a megaphone. I followed the direction of Jochen's pointed finger and saw Hamid standing some way off behind a parked car, taking photographs of the demonstrators.

We wandered over to him.

'Hamid!' Jochen shouted and he turned, visibly surprised at first, then pleased to see who it was greeting him. He crouched in front of Jochen and offered him his hand to shake, which Jochen did with some vigour.

'Mr Jochen,' he said. 'Salaam alaikum.'

'Alaikum salaam,' Jochen said: it was a routine he knew well.

He smiled at him, and then, rising, turned to me. 'Ruth. How are you?'

'What are you doing?' I said, abruptly, suddenly suspicious.

'Taking photographs.' He held up the camera. 'They are all friends of mine, there.'

'Oh. I would have thought they wouldn't want their photos taken.'

'Why? It's a peaceful demonstration against the Shah. His sister is coming here to Oxford to open a library they have paid for. Wait for that – there will be a big demonstration. You must come.'

'Can I come?' Jochen said.

'Of course.' Then Hamid turned, hearing his name shouted from the demo.

'I must go,' he said. 'I'll see you tonight, Ruth. Shall I bring a taxi?'

'No, no,' I said. 'We can walk.'

He ran over to join the others and for a moment I felt guilty and a fool, suspecting him in that way. We went into the Westgate to look for pyjamas but I found myself still brooding on the matter, wondering why anti-Shah demonstrators would be happy to have their photographs taken.

I was standing over Jochen as he packed his toys into his bag, urging him to be more ruthless in his selection, when I heard Ludger come up the iron stairs and enter through the kitchen door.

'Ah, Ruth,' he said, seeing me in Jochen's room. 'I have a favour. Hey, Jochen, how are you, man?'

Jochen looked round. 'I'm fine, thank you,' he said.

'I got a friend,' Ludger continued to me. 'A girl from Germany. Not a girlfriend,' he added quickly. 'She's saying she wants to visit Oxford and I'm wondering if she could stay here – two, three days.'

'There's no spare room.'

'She can sleep with me. I mean – in my room. Sleeping bag on the floor – no sweat.'

'I'll have to ask Mr Scott,' I improvised. 'There's a clause in my lease, you see. I'm really not allowed to have more than one person to stay here.'

'What?' he was incredulous. 'But it's your home?'

'My rented home. I'll just pop down and ask him.'

Mr Scott worked some Saturday mornings and I had seen his car was parked outside. I went down the stairs to the dentist's rooms and found him sitting on the reception desk, swinging his legs, talking to Krissi, his New Zealand dental nurse.

'Hello, hello, hello!' Mr Scott boomed, seeing me arrive, his eyes huge behind the thick lenses of his gold-rimmed spectacles. 'How's young Jochen?'

'Very well, thank you. I was just wondering, Mr Scott, would you object if I put some garden furniture out at the bottom of the garden? Table, chairs, an umbrella?'

'Why would I object?'

'I don't know – it might spoil the view from your surgery, or something.'

'How could it spoil the view?'

'That's great, then. Thanks very much.'

Mr Scott, as a young army dentist, had sailed into Singapore Harbour in February 1942. Four days after he arrived the British forces surrendered and he spent the next three and a half years as a prisoner of the Japanese. After that experience, he had told me – in all candour, without bitterness – he had made the decision that nothing in life was ever going to bother him again.

Ludger was waiting at the top of the stairs. 'Well?'

'Sorry,' I said. 'Mr Scott says no. Only one guest allowed.'

Ludger looked at me sceptically. I held his gaze.

'Oh, yeah?' he said.

'Yeah. In fact you're lucky he's let you stay for so long,' I lied, quite enjoying the process. 'My lease is at stake here, you know.'

'What kind of shit country is this?' he asked, rhetorically. 'Where a landlord can tell you who can stay in your home.'

'If you don't like it you can always bugger off,' I said, cheerfully. 'Come on, Jochen, let's go to granny's.'

My mother and I sat on the rear terrace of the cottage, looking out over the blond meadow at the dark green mass of Witch Wood, drinking home-made lemonade and keeping an eye on Jochen, who was galloping around the garden with a butterfly net, failing to catch butterflies.

'You were right,' I said, 'it turns out Romer is a lord. And a rich man, as far as I can tell.' Two visits to the Bodleian Library had furnished me with a little more information than the few facts provided by Bobbie York. I watched my mother's face intently as I documented Romer's life, reading from the notes I had made. He was born 7 March 1899. Son of Gerald Arthur Romer (deceased 1918). An elder brother, Sholto, had been killed at the Battle of the Somme in 1916. Romer had been educated at a minor public school called Framingham Hall, where his father had taught classics. During the First World War he had become a captain in the King's Own Yorkshire Light Infantry, and had won the Military Cross in 1918. Back to Oxford, post-war, to St John's College, where he obtained a first-class degree in history in 1923. Then there were two years at the Sorbonne, 1924-5. Then he joined the Foreign Office from 1926-35. I paused. 'Then it all goes blank, except that he was awarded the Croix de Guerre – the Belgian Croix de Guerre in 1945.'