The dead of Jericho by Colin Dexter

'Abingdon' was misspelt (the 'g' omitted), and each of the lines gradually veered from the horizontal towards the bottom of the envelope, as if the correspondent were not particularly practised in any protracted activity with the pen. Inside the cover was another envelope, of the same brand, folded across the middle, the name 'Charles Richards' printed on it in capitals, with the words 'Strictly Personal' written immediately above. Richards slit this second envelope with rather more care than he had done the first, and took out the single sheet of good quality paper. There was no address, no signature, and no date:
Dear Mister Richards
    Its about Missis Scott who died, I now all about you and her but does Missis Richards. I now ALL about it, I hope you believe me because if you don’t I am going to tell her everything, You dont want that. I am not going to tell her if you agree, You are rich and what is a thousand pounds. If you agree I will not bother to rite again, I keep all promises beleive that. The police dont now anything and I have never said what I now. Here is what you do, You go down to Walton Street in Jericho and turn left into Walton Well Road and then strate on over the little Canal brige and then over the railway brige and you come to a parking area where you cant go much further, then turn round and face Port Medow and you will see a row of willow trees, the fifth from the left has got a big hole in it about five feet from the ground. So put the money there and drive away, I will be waching all the time. I will give you a ring soon and that will be only once. I hope you will not try anything funny. Please remember your wife.
    Although the writing was crudely printed, with several words written out in individual, unjoined characters, the message was surprisingly coherent — and disturbing. Yet as Charles Richards read it, his mind seemed curiously detached: it was almost as if the writing had been submitted to him as a piece of English prose that had to be corrected and commented upon — its message secondary and of comparatively little significance. He read the letter through a second time, and then a third, and then a fourth; but if a hidden observer had recorded the conflicting emotions of puzzlement, anger, and even anxiety, that played upon his face, there was never the slightest hint of panic or despair. For Charles Richards was a clever and resourceful man, and he now refolded the letter, replaced it in its envelope and put it, together with the outer cover, inside his wallet.
    Five minutes later he waited for a few seconds by Celia's bedside as she sat up, drew a cardigan round her shoulders, and took the breakfast tray of orange juice, tea, and toast. He kissed her lightly on the forehead, told her that he had to go into Oxford, that he'd take the Mini, and that he'd certainly be home for lunch about one. Was there anything he could get her from the shops? He'd perhaps have to nip into Oxford again in the evening, too.
    Celia Richards heard him go, a great burden of anxiety weighing on her mind. How could a man so treacherous seem so kind? It had been an extraordinary coincidence that the first copy of the Oxford Mail she'd read for months had contained that account of Anne Scott's death, and she felt quite sure that Charles had read the article, too. Had he been responsible for that terrible thing? She couldn't really know and, to be truthful, she didn't care much either. What she did know was that their life together just couldn't go on as it had been. Putting things off was merely aggravating that almost intolerable burden, and she would put it off no longer. He'd said he'd be in for lunch; and after lunch... Yes! She would tell him then. Tell him all she knew; tell him the truth. It was the only way-the only way for her. Conrad had counselled against it, but Conrad would understand. Conrad always understood... She munched the tasteless toast and drank the lukewarm tea. Oxford... He'd always