A simple cache that is a tribute to the author who is probably the second one people think about at Christmas time. There is nothing to be found at the above co-ordinates, well nothing of any great import.
To find the cache you need to read, or listen to, the correct story and then answer the questions below:
When did the secretary send the first letter? : April ab
When did the secretary send the second letter? : April 1c
When did the secretary send the final letter? : April de
What year did John Harrington die? 18fg
How many months were allowed? h
What is Harley's ticket number? klmn
O = (d + l)
q = (m / d)
The cache be found at: N51 14.oeh W002 19.naq
Whilst the story can be found behind the Abbot's message.
The cache is large enough to take most TBs and geocoins.
There is a special prize awaiting the person who finds this cache first - an 8Gb USB memory stick containing a librevox recording of his tales. Whilst I have tried to ensure that the USB stick is free of viruses and other nasties, you should virus scan it yourself before reading it.
Merry finding all.

Congrats to somersetsmithys on being the first to find the Abbot's Christmas Box.
If you’ve enjoyed this puzzle then why not have a go at the rest of the puzzles in my annual M.R. James Christmas series:
2022 - Mr Dennistoun’s Discovery
2021 - The Dancing Advocate
2020 - Madam, will you walk?
2019 - Mr Garrett's Quest
2018 - Mrs Mothersole's hiding place
2017 - Mr Wraxall’s Last Expedition
2016 - Quis Est Iste Qui Venit
2015 - Penetrans ad interiora Mortis
2014 - Mr Britnell's Troublesome Object
2013 - The Abbot of Lufford's Christmas Box