The mission known as Prelude to Endor took place before the Battle of Endor. During this operation, Darth Vader apprehended Bothan spies who were involved in stealing information regarding the plans for the new Death Star from the Bulk freighter called Suprosa.
In the initial phase of this operation, Bothan prisoners were transported to Lord Vader via the Dreadnought named Dargon. The Rebels launched several attempts to disable the vessel and liberate the prisoners held within, but each attempt failed due to the intervention of the skilled Imperial pilot, Maarek Stele. Eventually, the Bothans were delivered to Vader's Star Destroyer, the Garrett, where they were interrogated.
Using the information obtained from the prisoners, the forces aboard the Garrett initiated a move to capture more Bothans who were involved in the capture of the Freighter Suprosa. Several Bothan Muurian Transports were disabled and seized at Bothawui, along with a shuttle carrying a high-ranking officer. New intelligence data led the Imperial forces to attack and capture the Bothan base at Kothlis, where Stele inspected the Corvette Timoth 4, which was carrying decoding equipment. This confirmed the Secret Order's suspicion that the Bothans were attempting to crack the supercomputer located on the Suprosa.
Following this, the Garrett's forces attacked a rendezvous point, resulting in the destruction of the Bothan Dreadnought Doomer and the capture of the Rebel Calamari Cruiser Knights. The Rebel Nebulon-B2 frigate Tarken arrived to assist, but was also captured.
After this success, the Secret Order's liaison informed Maarek Stele about the real purpose of the stolen Death Star plans: to mislead the Rebels into believing the second Death Star was not yet operational, when in reality, it was. This was a significant part of a plan to lure the Rebel Alliance to their ultimate destruction at Endor.
Stele was then dispatched on a reconnaissance mission to determine if there was a significant gathering of Rebel starships in the Delfii system. He inspected many ships, including the Calamari Cruiser Lutdze, which had Admiral Ackbar on board. He also received a task from the Secret Order to eliminate an Escort Shuttle carrying computer specialists who questioned the accuracy of the information regarding the Death Star's operational status.
As a final preparatory action before the Battle of Endor, Maarek Stele was given the task of delaying the Rebel fleet by destroying a number of their starships, along with a squadron of starfighters.
For his role in the campaign, Stele received the Medal of Guile. Lord Vader personally notified the Emperor that all preparations had been completed, and the trap was set to be sprung as soon as the Rebels arrived at Endor.