A pale, bespectacled gentleman took the pipe from his mouth and waved it vaguely towards me, ushering me in. ‘Thank you, Mavis. Please have a seat, Miss Buchanan. I’m very pleased to meet you.’ Although I didn’t know it at the time, Dilly Knox was ill with cancer when I first met him and only occasionally made the journey to the Cottage at Bletchley Park from his home, where he continued his work breaking the trickiest enemy codes. I suppose he must have come in specially for this meeting that day, and the girl I met must have been one of the team of crack cryptanalysts whom he had personally trained.
 
 He settled himself behind his desk and took a few puffs on his pipe, exhaling another cloud into the air of the already smoke-laden room. ‘Alan speaks very highly of you. And he tells me you have a Polish mother back in Scotland.’
 
 I nodded, still unsure as to why I was there.
 
 ‘He also tells me you are aware of the Polish mathematicians who helped us get to where we are with Enigma, is that correct?’
 
 ‘Well, yes, but I only know the barest of facts.’ I wasn’t sure what I should say, and that pistol sitting on the desk when I’d signed the Official Secrets Act was still etched on to my memory.
 
 He must have guessed what I was thinking because he smiled and said, ‘It’s all right, Miss Buchanan, within these four walls we can speak freely. But nothing I tell you today must ever be discussed with anyone else, not even your colleagues in Hut 8. Do you understand?’
 
 I nodded again. He was softly spoken, and the tone of his voice was mild, but I could sense the gravity of this conversation.
 
 He went on to tell me that the team of Polish cryptographers, whom he’d met in 1939 just as war was breaking out in Europe, had been moved by the French Intelligence – theDeuxième Bureau– to a château in the unoccupied Vichy zone in the south of France, where they were carrying on their work.
 
 ‘My contact in the Bureau tells me there are now about a dozen of them there,’ he said. ‘And they continue to provide us with some of the most important information about what the Nazis are up to. I’m keen to maintain the relationship we have with them because they’re such crucial allies in the fight to break the German codes. As you’ll be aware from your work in Hut 8, our enemies constantly keep us on our toes, frequently changing their cipher systems. The Polish team are some of the very best in the world at understanding German tactics and coming up with new ways to decipher the radio traffic.’
 
 I listened in silence, still unsure as to why he was telling me all this.
 
 ‘The Head of theDeuxième Bureauis keen to keep them in France. He’s gone to great lengths to secure a place for them at a base, a château code-named Cadix. We don’t wish to rock that boat. However, at this juncture, not only do we want to let them know how much we value their work, and the fact that they risk their lives every single day in order to further the Allied cause, but I personally want them to know we haven’t forgotten them. I have some materials I’d like to get to them,’ he said. ‘A few things that might help them in their work. Remind them that they have friends over on this side of the Channel too.’
 
 I was still silent, although I was beginning to suspect I could see where I might come in. My stomach began to flutter with nerves.
 
 As if he’d read my mind again, Dilly Knox continued, ‘So I need a courier. Someone who is entirely trustworthy. Someone who speaks their language. And I don’t just mean Polish. I meana mathematician, like them. A cryptanalyst who can talk to them about the progress we’ve made here with our codebreaking and can, in turn, understand anything they may care to share in terms of the techniques they’ve developed there.’ He peered short-sightedly at me over the top of his round-rimmed glasses, squinting through the smoke-filled atmosphere. ‘You, Miss Buchanan, fit the bill.’
 
 I met his gaze calmly, although my mind was clattering like one of our machines with what he’d divulged, circuits firing and thoughts whirring as I made sense of what was being asked of me.
 
 ‘How would I get these materials to them?’ I asked, focusing on the practicalities.
 
 ‘We have a method in place for inserting agents into Vichy France,’ he replied. ‘But firstly I have to ask, do you know what’s being asked of you? Do you think you could undertake such a mission? Do you understand the risks involved?’
 
 ‘I do.’ My heart drummed out a beat faster and louder in my ears than any teleprinter. Conflicting emotions surged through me. It wasn’t just fear at the thought of what I was being asked to do. It was excitement too. I was thrilled to think I might meet the Polish mathematicians, that the materials I’d be bringing them might help them in their work just as they had helped us with ours earlier in the game. And I was fascinated to find out what they were doing in their French château, under the very noses of the Germans. From newspaper reports I’d read, I knew the Vichy government in the southern third of the country was nominally French, but really operated as a puppet regime, complying with every hateful Nazi edict the Germans issued from Paris.
 
 I realised my hands were shaking, so I clasped them in my lap to steady myself. I didn’t want Dilly Knox to mistake my excitement for cowardice. Alan had told me it was Polish intelligence that had given him such a head start in breaking Enigma. What if the information I brought back could help us take another leap forward,foreshortening the war still more? It would be worth the risk. There was no doubt in my mind about accepting the challenge.
 
 ‘Very well. In that case, I’ll put everything in place. I’ll have to liaise with our French counterparts, but once we’re ready, I’ll let you know.’ He got to his feet and reached his hand across the desk to shake mine. ‘The Poles taught me a word:Dziekuje. Thank you. For all you are doing. Even though no one can ever know.’
 
 And with that I was dismissed. I went back to my digs and tried to carry on as usual, chatting to Mrs Webb about safe topics like the weather as I helped her peel potatoes for supper at the kitchen sink.
 
 ‘You look a bit peaky, dearie,’ she said. ‘Are you all right?’ She’d been very solicitous ever since I’d come back from Scotland after Teddy’s funeral, looking after me, offering me little extra bits and pieces to eat from the rations and a hot-water bottle for my bed, even though the nights were less chilly now. ‘Not bad news in that letter today, I hope?’
 
 Whenever a letter from Ben arrived, she’d leave it on the shelf in the hall beside the telephone, so it’d be the first thing I’d see when I got home.
 
 I patted the latest letter in my pocket, smiling at her reassuringly. ‘No, all’s well. I’m fine, thanks, just tired.’
 
 Jess was setting the table. Our shifts had synchronised again, which meant we enjoyed each other’s company in the evenings, sitting playing card games and chatting about safely anodyne topics, such as the best places in Edinburgh to buy shoes. She swivelled round and shot me a searching look, sensing something more perhaps. I shook my head very slightly, letting her know it wasn’t something I could discuss, like so much of what we did.
 
 Mrs Webb picked up a tea-towel and used it to open the door of the stove, lifting out the casserole she’d prepared. ‘They must work you girls ever so hard over at that place, doing all that filing and typing and whatnot,’ she said.
 
 Jess and I exchanged grins, while our landlady fished in a drawer for a spoon with which to stir the watery stew before popping it back into the oven to finish cooking, in the vain hope that the tough and stringy meat might soften a little. We were aware that there were various rumours circulating in the local community about what went on at the Manor, as it was known. These included the theory that it was either a home for knocked-up Wrens or that it really was a lunatic asylum, given the eccentric assortment of staff who came and went on their bicycles and buses every day.
 
 I smiled again and nodded, careful to give nothing away. ‘I think I just need a bit of fresh air,’ I said. ‘I’ll pop out for a walk – be back in time for supper.’
 
 I let myself out, shutting the gate behind me, and walked along the lane a way. It was May and the hedgerows were alive with wildflowers, bees buzzing busily from bloom to bloom, collecting nectar in the late-afternoon sunshine. There was something very reassuring about the normality of it all, in the peace of the English countryside.
 
 This is what we’re all fighting for, I thought as I walked. This freedom. All the simple, beautiful, everyday things became heightened when I set them against the very real risks I’d be facing. When I thought about the big picture – was I really about to be dropped into enemy France to smuggle materials to a team of Polish spies? – I felt completely overwhelmed. It was too much to contemplate. So instead I concentrated on the bees hurrying to make the most of the last of the day’s sunshine, and on the bluebells nodding their heads above constellations of starry white woodruff, on the first green spikes of wheat pushing through the brown earth in the field beside the road, and on the sounds of the birdsong and the scent of new-cut grass. I walked on, putting one foot in front of the other, telling myself that was all I had to do. When I reached the end of the lane, I perched on the wooden stile and took Ben’s letter from my pocket.
 
 Darling Philly, he’d written,