Scouting
Reconnaissance, Secret Investigation
noun, verbal noun
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.
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?
あのレストラン、税務署の内偵調査が入ったらしいよ。
I heard that restaurant was secretly investigated by the tax office.
探偵事務所に夫の浮気の内偵調査をお願いしました。
I asked a detective agency to secretly investigate my husband's affair.
京都府警が内偵を開始したらしいよ。
I heard the Kyoto Prefectural Police have started a covert investigation.