They go quietly, many at half pace (4)
I believe the answer is:
mice
'they' is the definition.
Both the answer and definition are plural nouns.
Maybe there's an association between them I don't understand?
'quietly many at half pace' is the wordplay.
'quietly many at' becomes 'mi' (I can't justify this - if you can you should give a lot more credence to this answer).
'half' indicates taking half.
'pace' cut in half is 'ce'.
'mi'+'ce'='MICE'
'go' is the link.
Can you help me to learn more?
(Other definitions for mice that I've seen before include "''Of ... and Men'' (John Steinbeck)" , "Domestic rodents" , "eg Mickey and Minnie" , "Blind group" , "operate computers" .)