Ota Gallo worked for the Office of Naval Intelligence for nearly two decades. However, in late 2553, she was recruited by Dark Moon Enterprises, a recently-established and rapidly growing private security corporation. At some point she contacted Spencer Hume, an investigative journalist who had recently been broadcasting exposés on ONI. Gallo fed Hume information on the SPARTAN-III program, particularly Gamma Company, in an attempt to undermine ONI for Dark Moon's gain. On October 14, 2553, Gallo, disguised as a server, infiltrated the officers' club at UNSC Recreational Facility 6055-NA-A on Neos Atlantis, where Veta Lopis and her Ferret Team were participating in a covert training exercise. Gallo also managed to enable Hume access to the club and he began talking to Olivia-G291, who was undercover as part of the training exercise. Gallo brought Hume a bottle of zantelle laced with nicothiotal, intending to drug Olivia in an effort to get information on the Spartan-IIIs. Gallo then spotted Veta Lopis and approached her to sell her a drink. Gallo recommended the Titan Smoke whiskey, but Lopis chose a two-tailed comet instead. Lopis found it strange that a bar server did not know the difference between a rocks glass and a doffer, but wrote it off as inexperience. Gallo brought Veta a dark, coppery liquid—which Lopis immediately recognized as not being a two-tailed comet, though she chose not to complain.
Shortly afterward, the effects of the nicothiotal began to show in Olivia's behavior. Realizing Olivia had been drugged, Lopis ordered Mark-G313 to get Hume out of the bar. Gallo tried to delay Mark by walking in front of him with a tray of drinks, but Mark shoved the tray into her chest and tripped her. Gallo's response, slapping her arms out and tucking her chin, suggested to Veta she had hand-to-hand combat training. Mark managed to capture Hume and headed for the emergency exit. Taking the server to be a part of their training exercise, Veta posed as a member of the Criminal Investigation Division, and had two ensigns hold Gallo as a witness to Olivia being drugged. However, Gallo managed to escape and went after Mark and Hume with a knife. Mark did not see Gallo coming as Hume was resisting, and instinctively used Hume as a shield to block the knife; however, Gallo still managed to slash Mark in the clavicle. When Hume continued to resist Mark punched him in the chest, killing him. By then Ash-G099 had arrived and Gallo retreated after throwing her knife at Ash. Mark and Ash disposed of Hume's body out an airlock and cleaned the scene.
Lopis and her team later discovered Gallo's identity and status after running Gallo's picture through ONI's Facial Recognition Database. Not wanting to let Gallo escape with information on the Spartan-IIIs, Veta lured Gallo to their hotel suite with Hume's COM pad. Gallo attacked the room with two other men, who were quickly taken down by Mark and Ash. Gallo then attempted to throw a grenade in the room, but not before Olivia threw a knife at her; Gallo was subsequently blown apart by the grenade in the lobby, while all members of the Ferret Team survived. Later upon meeting up with Rear Admiral Serin Osman, Lopis framed Gallo for Hume's murder, claiming Gallo killed Hume to prevent him from naming her as his source.
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