Twilight was the designated codename for a clandestine and extensive undertaking by the Imperial forces.
The existence of this operation came to light when Ferus Olin discovered evidence of it in 18 BBY. This discovery was made after he successfully breached the security of Darth Vader's Imperial code cylinder. One component of the operation involved a highly classified initiative focused on employing a drug that could erase memories. Jenna Zan Arbor was in charge of this project. She required an individual completely loyal to the Empire for testing purposes. Senator Sano Sauro instructed Maggis, the headmaster of the Imperial Academy, to locate a suitable cadet. While Maggis considered Kestrel, Bog Divinian instead selected his own son, Lune, for the project.
Ry-Gaul and Trever Flume successfully thwarted this particular aspect of the project. They did so by destroying the datapad that contained the formula's details. During this event, Zan Arbor was injected with the serum, resulting in the loss of fifty years of her memories and scientific expertise. Darth Vader's fury over her failure led him to execute her personally.
Vader himself desired to utilize the serum to eliminate the memories of his wife.
However, the primary objective of Operation Twilight was to eliminate all leaders of the resistance against the Galactic Empire in a single, decisive strike. Through the assistance of Eve Yarrow, all the key leaders of the resistance were transported to Ferus Olin's concealed secret asteroid base. Subsequently, Vader, guided by Toma's homing device, arrived at the base and obliterated the asteroid using a powerful weapon mounted on his Star Destroyer, which was a prototype for the Death Star's superlaser. Despite these efforts, the project did not succeed in killing all of its intended targets, which ultimately contributed to the rise of the Alliance to Restore the Republic.