According to the foreword of the edition of Wilkie Collins’ The Moonstone which I read (I regrettably forget the name of the writer of the foreword, and which edition I read– it was years ago. Sorry), The Moonstone is the first detective novel.
There are thankfully a great deal of good fictional murder mysteries and the like for us to read now, more than a hundred years later, and I admit to enjoying them on occasion.
I have found myself much addicted to the books of a French writer, Emile Gaboriau, and his Monsieur Lecoq mysteries. These are out of print (the Kindle is a bookworms’ second-best friend!), and Agatha Christie’s books are always good. But one particular, strange Kindle book that is rather obscure is Baroness Emmuska Orczy’s The Old Man in the Corner. Rather an odd ending on that (I won’t tell what), but perhaps it might be found interesting.
I hope you find something good to read. Enjoy!