Active Two was a United Federation of Planets covert surveillance team active in the year 2385. The team was headquartered in a building that officially was an unmanned networking hub facility in in San Francisco, California.
Active Two conducted covert surveillance on a number of individuals via drones and living beings; with its members parsing through intelligence gathered and sending it on to their superiors. Many of the individuals assigned to intelligence gathering were Vulcan due to their being better at concentrating and sifting through intelligence than other species.
After the promotion of William T. Riker to the rank of Rear Admiral in 2385, Active Two began conducting covert surveillance on him. One evening while Riker and his wife Deanna Troi were at dinner, Active Two placed a drone in the air high above the restaurant where they were eating and monitored the conversations the couple had over dinner. The Vulcan agent monitoring Riker noted to her surprise that someone with a higher clearance level had tapped in to the feed and was watching it live.
Active Two also had an individual tailing Riker, however he quickly became aware that he was being followed both at Starfleet Headquarters and out in San Francisco. (ST - The Fall novel: The Poisoned Chalice)