Not that it had been a lot of fun dealing with him. I must have spent hours working on the details, going over those ten moments in time, for example, making sure that they actually stitched together and that everything made sense. Most of the editing work was done over the Internet – Alan and I had always had a fractious relationship – but we did sit down together once in my London office and as I reread the book in the garden of Branlow Hall, I was reminded of the arguments we’d had on that long autumn afternoon. Why did he have to be so unpleasant? It’s one thing for writers to defend their work. But he would raise his voice and jab his finger and make me feel that I was somehow trespassing in the sacred fields of his imagination rather than trying to help him sell the bloody thing.

For example, I would have liked him to have opened with Atticus Pünd. It was his story after all, and I wondered if readers would put up with four whole chapters before they met him. Nor was I happy with the chapter entitled ‘The Ludendorff Diamond’, which really sits as a short story outside the main investigation and has nothing to do with what happens in Tawleigh-on-the-Water. I wanted to drop it but he wouldn’t listen. I might have rubbed a nerve because we both knew that, at seventy-two thousand words, the book had come in under length. This didn’t matter terribly: quite a few Agatha Christie novels are short. By the Pricking of My Thumbs and Death on the Nile (a masterpiece) both sit in the high sixties. Taking out the theft of the diamond would reduce the book almost to the length of a novella and might damage its commercial chances, but the simple truth was that Alan wasn’t prepared to do the necessary work to bulk out the rest of it so I was stuck with what he’d given me. I do like the chapter, by the way. It was my idea to put the tear in the wallpaper in Melissa James’s bedroom so that at least there would be some excuse for including it.

Our most serious disagreement concerned the character of Eric Chandler. Eric had struck me as a fairly unsympathetic creation, and this was some years before modern sensibilities would make any author think twice before introducing a disabled character. Giving a man a club foot is one thing. Making him an overgrown child with a sexual perversion seemed almost deliberately offensive, somehow equating disability with inadequacy. Of course, at the time I had no idea that he was based on Derek Endicott, the night manager at Branlow Hall. It was, as Lawrence Treherne had said, a particularly cruel caricature and if I’d known about him I’d have fought all the harder.

I also came to blows with Alan over a moment in the denouement. When Atticus Pünd visits Nancy Mitchell in hospital – after saving her life on the bridge – he tells her that he will always be her friend and wants to help her. And yet, a couple of chapters later, he accuses her of murdering Francis Pendleton. ‘He’s hardly very kind!’

‘He does it for effect!’ I still remember Alan sneering at me in that slightly superior way of his.

‘But it’s not in character.’

‘It’s a convention. The detective gathers all the suspects and he picks them off one by one.’

‘I know that, Alan. But does he have to pick on her?’

‘Well, what do you suggest, Susan?’

‘Does she even need to be in the scene?’

‘Of course she has to be in the scene! The scene won’t work without her!’

In the end, he softened it slightly – though with plenty of ill grace. I still didn’t like it.

And so it went on. As I’ve mentioned, Alan liked to hide things in his books and it occurred to me now that he might have fought against some of the edits I wanted to make because I was unknowingly removing some of the secret messages that were so precious to him: Easter eggs, I suppose you might call them now. I’ve already mentioned that I disliked the name Algernon because I thought it was a bit pantomime. I thought it was unlikely that Algernon would have been driving a French-manufactured Peugeot in 1953. I didn’t like the Latin numerals in the chapter called ‘Darkness Falls’. They seemed to me to be stylistically out of keeping with the rest of the book. And, for the same reason, I was unhappy with the real people who cropped up throughout the text: Bert Lahr, Alfred Hitchcock, Roy Boulting, and so on.

He refused to change any of these.

I also had problems with ‘Darkness Falls’ as a chapter title – and this was definitely one of his Easter eggs. Despite everything, Conway revered Agatha Christie and often stole ideas from her. ‘Darkness Falls’ and the descriptions of Tawleigh at night are an obvious riff on her novel Endless Night, just as another chapter, ‘Taken by the Tide’, pays homage to Taken at the Flood. Using Othello to plant a clue is very much in her style; after all, she named four of her novels after Shakespeare’s plays. She even makes a guest appearance in the text. On the train down to Devon, Miss Cain is reading the new Mary Westmacott, which was, in fact, Christie’s nom de plume.

It wasn’t just me. The copy editor got slapped down too. She had various issues, but one that I do remember was the LMR 57 steam engine that arrives to carry Pünd back to London in the final chapter. It was actually withdrawn a hundred years before the story takes place. It operated on the Manchester and Liverpool Railway rather than in Devon and it was mainly used for freight. Alan didn’t care. ‘Nobody will notice,’ he said and it stayed in. But why? Surely it wouldn’t have been so difficult to make the change. She also agreed with me that it would have been very hard to find a right-hand-drive Peugeot in 1953.

None of these discussions seemed to have any relevance to the question of who had actually killed Frank Parris, though. But the fact was, Alan knew the truth. He’d told his partner James Taylor when he got back from Branlow Hall, ‘They’ve got the wrong man.’ So why did he hide it? Why hadn’t he told the police? It was a question I had asked myself before, but after reading Atticus Pünd Takes the Case I was none the wiser, even if it now seemed that it contained not one but two sets of solutions between its covers. How could I get the book to unlock its secrets?

I began with the names.

Alan always played games with the names of his characters. In Night Comes Calling, the fourth Pünd novel, they were all English rivers. In Atticus Pünd Abroad, they were manufacturers of fountain pens. It didn’t take me very long to work out what he had done in Atticus Pünd Takes the Case. Although some of them are quite obscure, the names all belong to famous crime writers. Eric and Phyllis Chandler give it away. Obviously, that’s Raymond Chandler, who created Philip Marlowe, perhaps the most iconic of private detectives. Algernon Marsh comes from Ngaio Marsh, Madeline Cain from James M. Cain, who wrote The Postman Always Rings Twice and the wonderful Double Indemnity, Nancy Mitchell from Gladys Mitchell, who wrote over sixty crime novels – Philip Larkin was a fan.

But Alan had been cleverer than that. He had also linked each one of the main characters to the people he had met and interviewed at Branlow Hall, giving many of them the same initials and all of them similar-sounding first names. One example is Lance Gardner (from Erle Stanley Gardner), who had so offended Lawrence Treherne. Another is Dr Leonard Collins, who clearly has a connection with Lionel Corby (LC). By the same token, the Latvian producer Sīmanis ?aks must relate to Stefan Codrescu, although it’s interesting that he has almost no role in the book. He isn’t even really a suspect.

I realised that if I was going to work out what was going on in Alan Conway’s mind, I had to draw some sort of map between the worlds of Branlow Hall in Suffolk and Tawleigh-on-the-Water in Devon, and the most obvious landmarks were all these characters and their relationships both to each other and to their real-life counterparts. I had finished the book sitting at one of the tables outside the hotel, but now the sun had gone in so I returned to my room, grabbed a notepad and sketched out the following.

Melissa James

Name taken from: P. D. James, author of Innocent Blood and A Taste for Death. Or possibly Peter James (he provided a quote for the book!).

Character based on: Lisa Treherne, Cecily’s sister.

Notes: The characters have very little in common except for their first name: Lisa/Melissa. There is also one mention of the actress having a scar on her face (page 5). Lisa Treherne was possibly having sex with Stefan Codrescu, as seen by Lionel Corby. But in APTTC, Melissa is having an affair with Dr Leonard Collins.

Alan Conway’s wife was also called Melissa and she seems to have had a close relationship with the gym instructor, Lionel Corby (LC). Is Alan suggesting the two of them were having an affair?

Francis Pendleton

Name taken from: American crime writer Don Pendleton, author of The Executioner.

Character based on: Frank Parris.

Notes: As well as the shared initials (FP), Conway clearly connects Pendleton with Parris. They both have curly hair and dark skin and on page 10 of APTTC, Francis is said to own a sailing boat called Sundowner, which is also the name of Frank’s advertising agency in Australia.

Both men are murdered, one with a knife, the other with a hammer. Another connection. But there is nothing in the book that comes anywhere near Madeline’s motive for killing Francis.

Nancy Mitchell

Name taken from: Gladys Mitchell, author of the Mrs Bradley mysteries.