Arrest, finding weapon in bibliophiles' association (4,4)
I believe the answer is:
book club
'bibliophiles' association' is the definition.
'arrest finding weapon' is the wordplay.
'arrest' becomes 'book' (book can informally mean to arrest).
'finding' says to put letters next to each other.
'weapon' becomes 'club' (I've seen this before).
'book'+'club'='BOOK CLUB'
'in' is the link.
(Other definitions for book club that I've seen before include "Lit. Soc." , "literary gathering" , "Literary group" , "Society for readers" , "Society giving members cheaper access to reading material" .)