By definition, past perfect simple tense "expresses an action taking place before a certain time in the past".
I have a hard time to understand why Terry Pratchett used it in the sentence:
"The scythe that had done the work leaned against the gnarled bole of a pear tree."
Can I kindly ask for an explanation? I can't see any reason for it because no exact information about certain time in the past is given.
Thank you in advance.