The Holocron of Heresies, also known in simpler terms as Darth Andeddu's holocron, represented a Sith holocron crafted by the Dark Lord of the Sith himself, Darth Andeddu. Beyond housing Andeddu's lightsaber crystal, its most significant feature was the secret to transferring one's spirit into a different physical form. The inscription "In umbris potestas est" was etched onto the holocron utilizing the Aurebesh alphabet.
For countless years, it was lost to Sith history. The Sith holocron of Darth Andeddu was rumored to have been initially discovered by the fallen Jedi Freedon Nadd. During his quest to achieve eternal life, Darth Bane pilfered it from Andeddu's Keep on Prakith in 980 BBY, battling many of Andeddu's followers along the way. Because the gatekeeper refused to reveal the secret of immortality until Bane completed its "Games", Bane was forced to extract the essence transfer secret from the holocron. Set Harth then stole it from the Doan Royal House not long after. After centuries passed, the holocron eventually made its way back to Korriban. While trying to gain favor with Darth Tyranus, Quinlan Vos and Tol Skorr discovered the holocron sixteen months after the First Battle of Geonosis.
After acquiring the knowledge contained within the holocron, Tyranus dismantled the artifact and extracted a deep red lightsaber crystal that had been part of Darth Andeddu's lightsaber. He presented the ancient crystal to Vos and subsequently instructed him to travel to Coruscant to assassinate Senator Viento.
By 137 ABY, the holocron had come into the possession of Darth Krayt, the Dark Lord of the Sith and originator of the One Sith. Krayt activated the holocron with the intention of learning how Andeddu had managed to defy death, but the gatekeeper declined to advise the "pretender" on the grounds that Krayt had violated the doctrines of the Ancient Sith.
Darth Wyyrlok took the holocron to Andeddu's actual tomb, which was inside a keep located on the planet Prakith, while looking for a way to heal Darth Krayt. It was discovered there that Andeddu's holocron was unique from other holocrons. The holocron not only held Andeddu's complete intelligence (possibly his spirit), but it could also control the Force.
When positioned close to Andeddu's decaying remains, the holocron managed to drain the life force energy of Gerlun, who belonged to a Sith cult that went by the name of The Malevolence. The holocron then used Gerlun's life force to revive Andeddu's corpse. Due to Wyyrlok's own illusions, Andeddu lost control of his reanimated body. The Force-enhanced intellect was either obliterated or retreated back into the holocron.