Bow Street runner
FBI
FBI agent
G-man
Secret Service
Sherlock Holmes
T-man
agent
amanuensis
baggage agent
business agent
claim agent
clerk
commercial agent
commission agent
consignee
customer agent
detective
dupe
factor
fed
federal agent
freight agent
functionary
general agent
hotel detective
house detective
house dick
implement
inquiry agent
instrument
insurance agent
investigator
land agent
law agent
literary agent
loan agent
narc
news agent
official
operative
parliamentary agent
passenger agent
plainclothesman
police detective
press agent
private detective
private investigator
puppet
purchasing agent