Plan Delta was a putsch in 44 ABY orchestrated by the New Jedi Order against Natasi Daala, who was the Chief of State at the time. The aim was to bring an end to her increasingly despotic rule over the Galactic Federation of Free Alliances. Corran Horn, a Jedi Master, conceived and presented the plan, which ultimately resulted in Daala's removal from power, her subsequent arrest, and the establishment of a governing Triumvirate.
Following the conclusion of the Second Galactic Civil War, Natasi Daala, the Alliance Chief of State, fostered widespread anti-Jediism, holding the belief that the Jedi were no different than the Sith. This sparked a conflict between Daala and the Jedi Order, especially as a mysterious illness began to drive many Jedi insane, often leading to destructive outbursts.
Another issue emerged in the galaxy due to slave uprisings. Following the Klatooinian uprising against their Hutt masters, numerous other revolts occurred. Despite widespread support for abolishing slavery and growing support for the Jedi as Daala's regime became more draconian, Daala was determined to suppress the slave revolts, believing that order and stability were more important than the slaves' freedom. To achieve this, she tasked Mandalorians with ending the revolts. This controversial decision prompted the Jedi to side with the slaves, dispatching a fleet of StealthXs and numerous Jedi Knights to aid the slaves against the Mandalorians, such as during the Blaudu Sextus revolt. The Jedi's actions led Daala to suspect that they were responsible for the slave revolts, leading her to declare them her sworn enemies and declare war on them. The Jedi decided it was time to end her reign before more crimes were committed. Acting Grand Master Kenth Hamner wanted to try and convince Daala about the misunderstanding on Blaudu Sextus, but Saba Sebatyne felt that it's time that the Jedi stop kowtowing to Daala. In the midst of the argument, Han Solo revealed that Hamner had made a deal with Admiral Nek Bwua'tu in hopes that he could convince Daala to be reasonable, and was purposely stalling his fellow Masters, lying to them, in the vain hope that the admiral would awaken from his coma. This outraged the Jedi Council, who forwarded a vote of no-confidence and relieved Hamner of his position. Nonetheless, Hamner tried to stop the Order from launching StealthX to assist Luke Skywalker but died in the attempt. Consequently, the Council elected Sebatyne to lead them until Skywalker's return.
Unknown to both Daala and the Jedi, numerous influential political and military figures from both the Galactic Alliance and the Imperial Remnant also plotted to remove Daala from power. Led by Haydnat Treen, a Kuati Senator, and Drikl Lecersen, a Moff, they sought to merge the Remnant and the Alliance to create a new Galactic Empire. However, to achieve this, they needed to remove Daala from her position as Chief of State of the Alliance. In an attempt to position their people, they organized an assassination attempt on Admiral Nek Bwua'tu, the Head of the Galactic Alliance Defense Fleet, to replace him with Admiral Sallinor Parova, who also oversaw Fleet Security. To bring her closer to Daala, the conspirators orchestrated the poisoning of conspiracy members Lecersen and General Merratt Jaxton to discredit Galactic Alliance Security, prompting Daala to entrust her safety to Fleet Security.
The Jedi Council dispatched Seha Dorvald, a Jedi Knight, undercover as a pilot named Sela Dorn to infiltrate the Senate Building. There, she seduced Javon Thewles, a GAS Lieutenant, to facilitate the unloading of her cargo, which included Masters Kyp Durron and Octa Ramis. This would enable the two Jedi Masters to serve as sleeper agents for Plan Delta.
Meanwhile, the Imperial-Alliance conspirators seized the opportunity presented by these events. By exposing Dorvald's cover, they led Daala to believe that it was the beginning of a Jedi assault against her. Daala ordered the arrests of both Thewles and Dorvald. She believed Dorvald had become another insane Jedi, while she was safely in the Jedi Temple. Acting Grand Master Saba Sebatyne then asked Organa Solo to persuade Dorvald to turn herself to Daala. Unbeknownst to both the conspirators and Daala, this was another part of the Jedi plan: getting an agent in the lower levels of the Senate Building, namely the detention blocks. Thewles's supposed involvement led to Daala assigning her protection to Fleet Security and Admiral Parova, who were both a part of the conspiracy. To further fuel Daala's paranoia and madness, the conspirators used recently captured Klatooinian terrorist Grunel Ovin, allowing him to escape and cause the explosion of the CC-7700 frigate Fireborn in the planet's orbit. In response, Daala ordered the eradication of the gathering of freedom fighters on Klatooine by way of the Mandalorians.
Upon learning of this and unwilling to allow Daala's megalomania to result in further massacres, the Jedi immediately initiated Plan Delta. Using the Solos and the Millennium Falcon to infiltrate the Senate, Saba Sebatyne, Corran Horn, and Jaina Solo made their way to the Senate chamber where the Senate was gathered. The Solos themselves headed for Daala's office in guise of having a meeting with them. As a way to distract Daala, Sebatyne had Bandy Geffer rescue Dorvald from her cell and cause a simulated attack in the detention block. At the same time, Parova and Fleet Security were about to have Daala deposed when the Solos took the waiting room hostage after they were refused access to Daala's office. During this time, Sebatyne, Horn and Solo reached the Senate chamber where they intend to inform the Senators of Daala's arrest.
Realizing that their scheme had failed, Senator Treen approached Sebatyne privately and proposed forming a coalition transition government. Recognizing that this would garner support in the Senate, Sebatyne agreed.
Meanwhile, Daala attempted to flee with her Fleet Security escort, only to be stunned in the back by them. Parova then surrendered to the Solos and presented Daala, claiming that she had accidentally been stunned by one of Solo's bolt.
The Senate suspended the office of the Chief of State and established a new transition government, a Triumvirate consisting of Sebatyne, Senator Treen, and General Jaxton, to represent the interests of the Jedi, the Senate, and the military. They imprisoned Daala in the Armand Isard Correctional Facility, and Wynn Dorvan was tasked with finding a world that would give Daala a fair trial.
The coup also ended Luke Skywalker's sentence, so he could return to the Jedi Order and Coruscant whenever he desired.