He breaks down in the course of an investigation (7)
I believe the answer is:
analyst
'he breaks down in the course of an investigation' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he breaks down in the course of an' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'ly' and 'ly' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'course' could be 's' and 's' is present in the answer.
'an' could be 'a' and 'a' is found within the answer.
The remaining letters 'na' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for analyst that I've seen before include "One may look at chemicals" , "Person who interprets system structures" , "One examining in detail" , "one involved in breakdown" , "Dissector" .)