Much of what humanity knows about Isis comes from the ancient Egyptian religion and myth, however, a few individuals of the World of Darkness are aware of the account called "The Isis Fragments", in which this powerfull character describes her life.
The fragments say she lived in the beginnings of time, when gods walked the Earth, and although she answered by many titles - like Weret-Hekau, the Great of Magick and Mut-Netjer, the mother of gods - her name was Eset, but she would became widely known as Isis. In her account tells she came from a family of gods, were her forefather was Ra, the everlasting sun himself. She spoke with Ra in her dreams and through these dreams she gained power.
Isis and her husband-brother Osiris (champion of the Ma'at), were the protectors of their people and the land called Khem, which was the very first land created by the gods, while their culture was the first and best to grace the Earth. However, according to Isis there was a viper nested in Osiris court, and this viper attended by the name of Set, Osiris' younger brother and a cunning master of guile who coveted his power.
Through his manipulations, Set tricked Osiris' servants to imprison their king inside a sarcophagus made of gold and scented wood, prompting Isis and her son Horus to take shelter in the island of Chemmis, accompanied by the guardian Sebek (who, at the time, was the chieftain of the crocodile-folk who lived in the river Nile), the vampire Wadjet, and some of the Children of Bubasti.
Set eventually hacked Osiris to pieces and scattered his remains, conquering the throne of their nation and dominating the land unopposed. He finally found Isis and her son and captured them as well, changing Sobek into and Abomination in the process, damning the once proud Mokolé to exist as an unholy mockery of all what his kind stands for. In the aftermath of his tryumph, Set proceeded to torture mother and son, and it is said that Horus only survived because his mother kept him alive through the use of magic.
Then the wizard Thoth came, and taught Isis and Nephthys the ways of life and death, respectivelly. Isis desperately searched for her husband's body parts. When she collected all of the parts she could find of Osiris, her and the Children of Osiris, gave of their blood to their founder to restore him. His flesh mended together, becoming whole again, regaining consciousness even through Final Death.
When Osiris returned, Horus was too weak from his toil, but Anubis had teached his father how to finally heal the grievous wounds, but first, the boy needed to die. They used Mestha, their host, as a willing test subject and when the old farmer managed to return, they used the spell on Horus. In this moment, Set arrived and clashed with his siblings. He killed Nephthys and battled Osiris, who was aided by various shape-shifters who had observed Set's vile deeds and chose to act against his tyranny. Yet in the end, the Antediluvian was again victorious, consuming his brother's corporal form with magical fire, while preparing to kill Isis.
At this dire hour, Horus rose and defiantly stood against his uncle, slashing him with a great knife repeatedly until he emasculated him. In a powerful slash Horus destroyed his own eye, who had been in the posession of the vile vampire lord, dissipating much of his Ba trapped within and making his own Ka fade. Set had been temporarily defeated, but even he lay there, writhing, they could see that the Antediluvian was already healing. Using the time bought by Horus, Isis and Mestha fled to the Silent Striders, who granted them shelter, while taking Horus' body with them. When Horus rejoined his mother, he had reclaimed his Ba and stood before Isis as a worthy chieftain, a general in the war against Apep, the demonic serpent.
After they escaped, Isis gathered around her the men and women talented in the arts of Hekau, mentoring them as Thoth had mentored her, and creating allies and companions to her son Horus should he, the next time he died, have trouble resurrecting himself. As an old woman, Isis chose not to become a recipient of the Great Rites, that when she died she could join her husband and sister in Duat, and might advise and counsel her beloved in wiping free the land from Set's acrid stain.