Those against theft of lemurs (10)
I believe the answer is:
conspiracy
'of lemurs' is the definition.
The definition suggests a singular noun which matches the answer.
'those against theft' is the wordplay.
'those against' becomes 'cons' (I've seen this in another clue).
'theft' becomes 'piracy' (piracy is a kind of theft).
'cons'+'piracy'='CONSPIRACY'
Can you help me to learn more?
(Other definitions for conspiracy that I've seen before include "scheme" , "that involves plotting" , "intrigue" , "Plot" , "This is intriguing" .)