Intention that criminal cases citywide plummet (7)

I believe the answer is:
concept
'intention' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'criminal cases citywide plummet' is the wordplay.
'criminal' becomes 'con' (short for convict).
'cases' means to remove the middle letters.
'plummet' becomes 'pt' (I can't justify this - if you can you should believe this answer much more).
'citywide' with its centre removed is 'ce'.
'con'+'ce'+'pt'='CONCEPT'
'that' acts as a link.
Can you help me to learn more?
(Other definitions for concept that I've seen before include "Notion" , "Abstract or general idea" , "Product of the mind" , "Abstract idea; mental picture" .)