During the third annual cycle of the Clone Wars, the Advanced Recon Commando known as "Fives" fled Tipoca City located on Kamino. This escape occurred as he was actively trying to unravel the mystery surrounding the sudden actions of his comrade, Tup, who inexplicably murdered a Jedi Master. Fives' flight was prompted by the realization that his memories were in danger of being erased due to his knowledge of the biochip discovered within Tup's brain. He was aided in his escape by the droid AZI-3, and later returned covertly to have his own chip removed, confirming the presence of these chips in all clone troopers.
In the midst of the Battle of Ringo Vinda, CT-5385, known as "Tup," experienced a malfunction. This malfunction caused him to prematurely execute Order 66, resulting in the death of Jedi General Tiplar. Following an initial assessment of the clone, the Galactic Republic dispatched him to a medical facility on Kamino with the intention of determining the cause of his unusual behavior. While Tup was undergoing treatment, ARC Trooper CT-5555, also known as "Fives," located and extracted what he believed to be a tumor from Tup's head in a desperate attempt to save his friend. However, Tup died immediately after the procedure, and Fives was subsequently placed under arrest by Jedi General Shaak Ti. After the discovery of the tumor, Shaak Ti contacted Supreme Chancellor Palpatine to inform him of the discovery, and the Chancellor ordered that the tumor be sent to the Grand Republic Medical Facility on Coruscant.
After her conversation with Palpatine, Shaak Ti returned to the holding cell where Fives was confined. She then issued an order that the tumor be transported to the Jedi Temple instead of the Grand Republic Medical Facility, as the Chancellor had originally directed. Shaak Ti then informed Fives that he was required to undergo a final physical examination before being redeployed to the front lines. During the journey to the supposed examination room, the medical droid AZI-345211896246498721347, also known as AZI-3, disclosed to Fives that he was actually being taken to have his memory wiped and be reassigned to sanitation duties on Kamino. Upon learning this, Fives quickly incapacitated the clones who were escorting him and made his escape, accompanied by AZI-3. After an alarm was triggered, Fives rushed back to his former holding cell and retrieved the tumor from a case that had been switched.
Now in possession of the tumor, Fives quickly made his way to a hangar. There, he subdued a clone pilot in order to commandeer a ship. Just as Fives was boarding the vessel, Shaak Ti arrived with a contingent of clone troopers. However, she was unable to prevent Fives from stealing the ship. After successfully stealing the ship, Fives set the vessel on autopilot and then, along with AZI-3, jumped into the ocean below. After returning to Tipoca City with AZI-3's assistance, Fives re-entered the city and stole the armor of a passing clone trooper to blend in more effectively. Fives then instructed AZI-3 to further examine the tumor. This led AZI-3 to take Fives to the genetic records hall where they could compare the DNA in the tumor to that of Jango Fett. AZI-3 then proceeded to compare the samples but found no similarity whatsoever. This discovery led AZI-3 to believe that the tumor was, in fact, an implant rather than a natural brain tumor.
Driven by the need to determine if he also had the same implant as Tup, Fives and AZI-3 fled once more, heading to a medical chamber where AZI-3 performed surgery on Fives to extract the suspected implant. After discovering and removing the implant from his own brain, Fives sought to ascertain how widespread the implants were. Based on AZI-3's suggestion, they proceeded to the facility where clones in the early stages of development were being cultivated. Upon examining several clone embryos, AZI-3 discovered that all clones had these implants embedded in them from birth. At that moment, Doctor Nala Se entered the room, having been alerted by two Kaminoans that Fives and AZI-3 had trespassed. Fives confronted her about the implants in the clones, to which Se responded that they were inhibitor chips designed to limit the aggressiveness that was present in Jango Fett. Following this revelation, Shaak Ti and a group of clone troopers entered the room. Fives held Se at gunpoint. After an exchange during which the evidence Fives had collected was presented to Shaak Ti, she ordered him and all the evidence to be taken immediately to Coruscant.
During the journey to Coruscant, Nala Se secretly administered an unidentified drug to Fives before his scheduled meeting with the Chancellor. Once they were alone at the meeting, Palpatine revealed to Fives the true purpose of the control chips. This led to Fives being falsely accused of attempting to assassinate the Chancellor, which forced the rogue ARC trooper to flee the Grand Republic Medical Facility and become a fugitive. Fives eventually learned that the 501st Legion had returned to Coruscant and confronted Kix at the clone cantina 79's, giving him the coordinates for a location on Level 1325 where he hoped to meet with Clone Captain Rex and Jedi General Anakin Skywalker so he could reveal the truth about the situation.
However, Fives was spotted and tracked by a probe droid, which alerted the Coruscant Guard. When Skywalker and Rex arrived at the abandoned warehouse indicated by the coordinates, they found themselves trapped within a ray shield set up by a paranoid Fives. He attempted to explain the chips and their purpose but was unable to articulate himself coherently due to the drug administered by Nala Se, making him sound delusional. When Commander Fox and his troops arrived in response to the probe droid's report, the paranoid Fives reached for one of Rex's blaster pistols and was fatally shot.
With both Fives and Tup dead, Palpatine attributed the entire sequence of events to a parasite that the clones had contracted on Ringo Vinda, leaving the Jedi ignorant of the true nature of the "inhibitor" chips that would ultimately lead to their downfall.