Harris had been a member of Starfleet Security until 2149, at which point his official record ended.
Harris had entered into a covert alliance with Krell, a Klingon fleet admiral, who was attempting to contain an outbreak of a deadly plague which was sweeping throughout the Klingon Empire. Harris agreed to facilitate the abduction of Doctor Phlox to Qu'Vat Colony, where Phlox was to assist Doctor Antaak in developing a cure. In exchange, Krell led Harris to believe that both the Empire and Starfleet would benefit. When then-Lieutenant Reed began investigating Phlox's kidnapping, Harris contacted his old student, ordering him to stall Enterprise so that Phlox could complete his "assignment." When Reed asserted that he did not work for Harris anymore, Harris told him that Section 31's "recruitment policy" did not allow agents to leave.
Reed reluctantly carried out his assignment, and attempted to sabotage Enterprise's mission to find Phlox, but his treachery was discovered by Captain Archer, who had Reed put in the brig. Eventually, Reed informed Archer about Harris, and Archer told Reed to put him in contact with Harris. Reed did so, and Harris told Archer that, if Phlox was successful in finding a cure to the plague, the Klingon Empire would stabilize, which would be a benefit to Starfleet. Archer, however, was suspicious of Harris' motives.
When Harris contacted Krell to inform him that Enterprise was en route to the colony, Krell informed Harris that he never intended to honor their original agreement, and was planning to destroy the colony. Eventually, however, the starships Enterprise and Columbia NX-02 were successful in saving the colony, and Phlox was able to cure the plague. Afterward, Harris contacted Reed again, but Reed rebuffed him, saying that he only answered to his commanding officer, Jonathan Archer. (ENT: "Affliction", "Divergence")
However, barely a month later, Reed contacted Harris for information concerning Susan Khouri, a nurse who had worked for Terra Prime. Khouri had been killed attempting to deliver information on the daughter of Commanders Tucker and T'Pol, whom had been created as a binary clone. At the request of Archer himself, Reed asked Harris for all the information he had on the infant, and Harris agreed, but only on the condition that Reed would willingly work for Harris again. (ENT: "Demons")
Harris and Reed
Harris supplies Reed with information
Later, Reed contacted Harris for help in approaching Terra Prime's base on Mars undetected. Harris informed him that, due to terraforming, Mars' atmosphere was much thicker than the detection grid was originally designed for, and that a shuttlepod would be able to approach undetected as long as it stayed close to the surface, but that they would still need to reach the surface undetected. When Reed told him that they had devised a way to accomplish that without Harris' help, Harris responded by saying, "The student has surpassed the teacher," before wishing Reed good luck. (ENT: "Terra Prime")
Star Trek: Enterprise: (4)
Season 4 , Episode 15 "Affliction" (First appearance)
Season 4 , Episode 16 "Divergence"
Season 4 , Episode 20 "Demons"
Season 4 , Episode 21 "Terra Prime"