spy

secret

Something you know but do not tell other people.

police

The official group of people whose job is to stop crime and keep people safe.

agent

A person whose job is to do something for another person, a company or a government.

hide

To put something where it cannot be seen, or to go where no one can find you.

watch

To look at something for a time to see what it does or what happens.

scout

A person sent ahead to look at an area and bring back information; also a member of the Scouts youth group.

surveillance

Watching a person or place carefully and secretly, often by police or cameras.

undercover

Working in secret with a false name or job, so that nobody knows who you really are.