Plan from first of spies about to cross border (6)
I believe the answer is:
schema
'plan' is the definition.
(schema is a kind of plan)
'first of spies about to cross border' is the wordplay.
'first of spies' becomes 's' (cst letter of 'spies').
'about' becomes 'a' (abbreviation in Chambers).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'cross border' becomes 'chem' (I can't justify this - if you can you should give a lot more credence to this answer).
'a' put after 'chem' is 'chema'.
's'+'chema'='SCHEMA'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for schema that I've seen before include "essential form" , "Outline plan or theory - he's Mac (anag)" , "Synopsis" , "Outline or model of a technical plan or theory" , "Proposed arrangement" .)