detective; investigator; sleuth; detective work; secret investigation
spy; secret agent; spying
detective bureau; detective agency; investigation firm
detective team; study group; club
secret investigation; private enquiry; private inquiry; reconnaissance; scouting
reconnaissance plane; spy plane
detective work; detective industry
surveillance drone; unmanned reconnaissance plane
reconnaissance satellite; spy satellite
player put on starting list to be replaced by another when the opponent's pitcher is known
spying out; discovering (by covert investigation)
reconnaissance in force; combat reconnaissance