infiltration, sneaking into
Infiltrate a spy into the police force that uses spies and have them feed us information.
— M - Eine Stadt sucht einen Mörder (1931)
The person who took my picture was also the spy who infiltrated the place.
— イングリッシュ・ペイシェント (1996)
スパイがカイロに潜入ロンメルも地図を利用砂漠にバス路線を引いたも同然だ
A spy infiltrated Cairo, and Rommel used the maps—practically the same as laying bus routes through the desert.
— イングリッシュ・ペイシェント (1996)