The person wandering round inside is prying (7)
I believe the answer is:
snooper
'the' is the definition.
I can't tell whether this defines the answer.
'person wandering round inside is prying' is the wordplay.
'person wandering' becomes 'ser' (I can't justify this - if you can you should give a lot more credence to this answer).
'round' is an insertion indicator.
'inside' means to look at the middle letters.
'is prying' becomes 'snoopy' (synonyms).
The middle letters of 'snoopy' are 'noop'.
'ser' going around 'noop' is 'SNOOPER'.
Can you help me to learn more?
(Other definitions for snooper that I've seen before include "Prying investigator" , "Paul Pry" , "Furtive investigator" , "Prying person" , "Nosy individual" .)