IT isn’t every day you get to trace your fingertip across the signature of Dame Agatha Christie. But there it is – the actual signature of the woman who became the best-selling novelist in history, the author of 66 detective novels and dozens of plays and short stories: the creator of Miss Marple, and Hercule Poirot, and The Mousetrap.

The letter, on blue notepaper and dated March 16, 1941, refers to her wish for a specific dedication in her forthcoming novel, Evil Under the Sun. It is signed Agatha Mallowan: she took the surname from her second husband – the archaeologist Sir Max Mallowan, whom she met on an archaeological dig in 1930. The part with the address – 20 Lawn Road Flats – was at one time torn off, but fortunately not lost. And the addressee is none other than Billy Collins, the leading publisher who in 1924 lured the Queen of Crime to Collins – an arrangement that turned out to be highly profitable for both. The story goes that Christie had left her previous publisher after a dispute about the spelling of coco/cocoa.

2017, as it turns out, is a landmark year for HarperCollins, one of the world’s biggest publishers. It was in 1817 that one half of the enterprise, J&J Harper, was established in New York and published its first book, an English translation of Seneca’s Morals. Two years later, across the Atlantic, in Glasgow, Chalmers & Collins Bookshop and Printing Works published its first book, The Christian and Civic Economy of Large Towns by Dr Thomas Chalmers. The Collins was William Collins, a Pollokshaws teacher; the Chalmers was Thomas's brother, Charles.

For generations afterwards, both publishers – Harper in the States, Chalmers/Collins over here – broke new ground and published works by distinguished authors; their ranks included CS Lewis, Alexander Solzhenitsyn, Dr Seuss, Harper Lee, Boris Pasternak, John F Kennedy and Tolkien. Rupert Murdoch’s News Corporation bought Harper & Row in 1987 and Collins two years later, giving rise to the sprawling global behemoth of HarperCollins.

To mark the bicentenary, the publishers’ colossal archives have been mined, and many of the results can be seen on a dedicated website, 200.hc.com. And if you make your way to Collins’ own basement archives at HarperCollins at Bishopbriggs, you can see some of the jewels for yourself. Including that tantalising letter from Dame Agatha.

“The letter to Billy asks for Evil Under the Sun to be dedicated to someone called John, ‘in memory of our last season in Syria’”, says senior archivist Dawn Sinclair, 31. “She spent a lot of time in that part of the world, because her husband was an archaeologist. A lot of her books were set in Baghdad, or Syria, or Egypt, all based on her experiences of being there with Max and doing lots of adventuring with him.

“Agatha’s an important part of our history. William Collins published The Murder of Roger Ackroyd [a very early case for Poirot] in 1926 and after that we pretty much continued publishing her. Her success was quite intense and by the 1930s we had started the Collins Crime Club and as the Queen of Crime she was involved in that, though she also had books in the club’s precursor, the Detective Club”.

Research into the Christie-Collins letters by Sinclair’s colleague, Louise Neilson reveals “evidence of the beautiful friendship” between publisher and author, though Christie “paid Billy few courtesies when she was unhappy with the handling of her novels”. Yet they remained close, and when Christie died in January 1976, Collins spoke at her funeral, unaware that he himself had only nine more months to live.

Another of Sinclair's favourites in the archive concerns Boris Pasternak, the Moscow-born Nobel Laureate, author of such much-loved works as Dr Zhivago. “I’m really interested in Pasternak because I studied Russian at university”, she says. “When I found Pasternak material here I thought this was the most exciting thing ever. Collins had bought Harvill Press in 1953 and they had a lot of dissident writers and because of them we got Pasternak and we published Solzhenitsyn too.”

One letter in the archives reveals that in the 1950s, when Pasternak was ill, Billy Collins and Harvill contacted the Russian government, offering to pay for him to be flown to Britain for medical treatment before being returned to Russia, all without publicity.

The archive item in front of Sinclair today is a Russian copy of The Blind Beauty, a sequel to Zhivago. The manuscript was passed to Billy Collins by Olga Ivinskaya, who had been the author’s inspiration for Zhivago. “It’s a play, and it was going to be in three parts”, Sinclair says, “but he died in 1960 before he could finish it. I’d never heard of The Blind Beauty. We published it in 1969. This little Russian edition by Collins is one of only 50 copies that were ever made. We also published it in English, though it didn’t do particularly well. But when I found this, I let out a little scream – it really is that exciting”.

Another intriguing item relates to the Collins family itself. It’s a diary from 1837, written by William Collins the second when he was aged 20; in later life he would be a Lord Provost of Glasgow. It’s headed The Journal of a Visit to London in the Summer of 1837 by a Young Traveller and is dedicated to his father, with whom he made the trip to what he terms “the metropolis of this Empire”.

Sinclair leafs through the small diary. “They started from Glasgow on Tuesday, June 27, at 4pm and after a very pleasant drive they reached Edinburgh at 9pm – five hours later – and the next morning they got on a boat and sailed down the coast to London. Essentially the rest of the diary is what William did in London from day to day – he saw so-and-so, they walked down this famous street, that sort of thing”.

The diary was published by the firm, though for private use only. “A lot of representations of that particular William are of him as an older man; you’ll see pictures of him with a big beard, and that’s how he’s remembered. But this book is him when he was a young man, and going down to London with his dad. I have to say that although I’m incredibly interested in the history of publishing, and I love the stories about the authors and the books, I do love the history of the Collins family”.

It was in 1958 that Michael Bond, then a BBC TV cameraman in his early 30s, wrote a book about a little bear called Paddington. Sinclair’s favourite item is a series of mock-ups for the cover of the sixth book in the series, Paddington Marches On, which came out in 1964. The different layers together show that deciding on a book cover was not the work of mere moments: rather a lot of work went into it. And it’s quite a thought that Bond, who is now aged 91, is still published by HarperCollins today.

From the 1840s onwards Collins was an innovator when it came to dictionaries and Bibles. The dictionaries covered a mass of subjects and came in all sizes. Essentially, Sinclair says, “it was all about the first William Collins and his taste for dissemination of knowledge to the masses – he wanted everyone to have access to books and education.

"He had originally been a millworker and then a teacher, and he opened his publishing house because he wanted to make sure that it wasn’t just people with money who had access to knowledge”. The dictionary is a particularly ornate (its cover a rich blue) and beautiful old book.

Dawn Sinclair clearly adores her job and the privileged opportunities it gives her to handle documents that late, great authors have themselves touched. Like that letter from Christie, say. “I remember”, she adds, “coming across a contract with Ray Bradbury for Fahrenheit 451. And when I found that, and it had his signature on it, again I let out a little scream, because I just love Ray Bradbury.”

• http://200.hc.com/