Plot to put 100 at top of steeple (8)
I believe the answer is:
conspire
'plot' is the definition.
(I know that conspire is a more specific form of the action plot)
'put 100 at top of steeple' is the wordplay.
'put c00' becomes 'con' (I can't justify this - if you can you should give a lot more credence to this answer).
'at top of' says to put letters next to each other (in a down clue, some letters go on top of others).
'steeple' becomes 'spire' (synonyms).
'con'+'spire'='CONSPIRE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for conspire that I've seen before include "implicated in plot" , "scheme" , "Secretly plan together" , "'Plot, connive (8)'" , "Act secretly with others" .)