Agency Plant
When a spy organization, like the CIA or MI6, embeds an informant into some evil group bent on world destruction. Like, when James Bond goes undercover, but still just gives his name as "Bond. James Bond." (Don't these evil corporations ever do background checks? He's just using his real name.)
That's one form of agency plant. More commonly in the real world, though, "agency plant" has to do with insurance.
An agency plant refers to how big a sales and distribution footprint an insurance company has. The "agency" part has to do with the number of agents the company has working, either directly for it or as affiliated independent agents. You can think of the "plant" part anyway you want, like plants in the ground (you know, like roots and stuff), or like "hey, I'm working down at the plant today." Either way, the point is that the agency plant represents how broad an insurance company's operations are.