Reconnaissance, Secret Investigation
Noun and する verb
ないてい
警察はどんな時に内偵捜査をするのですか。
When do the police conduct their secret internal investigation?
Inside spying is when you get inside enemy territory and spy on them. This is scouting and reconnaissance.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.