Mole, e.g.

SPY

Think of someone who works undercover to gather secret information for an organization.

The clue "Mole, e.g." plays on the double meaning of "mole." In everyday language, a mole is a small burrowing animal, but in espionage, it refers to a spy embedded in an organization. Here, "e.g." hints that the answer is an example of the second meaning, so "SPY" fits perfectly. It’s a straightforward example of how crosswords use alternate definitions to misdirect slightly.