Case study number one — beginning of talks between soldiers on both sides (11)
I believe the answer is:
reconnoitre
'case' is the definition.
(I've seen this before)
'study number one beginning of talks between soldiers on both sides' is the wordplay.
I cannot really understand how this works, but
'study' could be 'con' (con can mean to study) and 'con' is found within the answer.
'number' could be 'i' (I is an example) and 'i' is found in the answer.
an anagram of 'one' is 'eno' which is present in the remaining letters.
'soldiers' could be 're' (Royal Engineers) and 're' is found in the answer.
This explanation may well be incorrect...
(Other definitions for reconnoitre that I've seen before include "Survey area" , "Act as a scout" , "Examine in advance" , "Check out" , "case" .)