She was raised in secret after the assassinations of her father and Janos Marik. However, rumor of her existence circulated and her mother was persuaded to present her as Thomas's child in early 3036. With her DNA proving she was indeed his child, problems lay ahead. Political technicalities of Thomas never formally taking the throne caused debate in Parliament on if she qualified to be his heir. However, this changed when Thomas Marik appeared on Atreus in December that year. Since Isis had been born illegitimately, she was passed over in the line of succession when her younger half-brother Joshua Marik was born in 3048. (In reality, of course, Thomas Marik would want his true biological heir to inherit the throne.)
Although she did fall in love with both Sun Tzu and his nation, years dragged by as her engagement with Sun Tzu continued awaiting for permission to marry.
Sun Tzu eventually began to feel tired of Isis and her lack of understanding of what it meant to be Capellan. Seeing that her political usefulness was coming to an end, he decided to make what use he could before discarding her. First sending her to the world of Hustaing as part of a tour of the region near the St. Ives Compact, Sun Tzu secretly arranged for a sleeper agent in the Blackwind Lancers to have the unit attack the world and hopefully assassinate his former fiancee. This act triggered the Capellan-St. Ives War, to reunite the state with its renegade commonality. Isis however survived the initial attack due to the bravery of Li Wynn, a Capellan infantryman from Warrior House Hiritsu.
During her six weeks on the run from renegade St. Ives troops on Hustaing, Isis befriended Jade Hollister, who had connections to an underground movement and taught Isis much about leadership and decision making. Tragically, Isis would accidentally shoot Jade Hollister in a firefight with rebel forces shortly before her rescue. The lessons learned in the six weeks on Hustaing, including death, killing, injury and frequent combat with regular and rebel troops and crime syndicates and ultimately the accidental killing of Jade Hollister turned Isis Marik into a tough, responsible and headstrong person.
Isis returned to Sian for the duration of the war. Ultimately, however, Sun Tzu dismissed her and had her ordered off-world and out of the Confederation.
Now in exile, Isis traveled to Mogyorod, where she took up an earlier offer to stay with Victor Steiner-Davion and Omi Kurita. She was in deep shock, still in love with Sun Tzu and being suddenly kicked out of the only home she had known. During the night, she spied a figure crawling through the mansion she shared with Omi and Victor. Initially, she thought it was an assassin sent by Sun Tzu to kill her; but instead, she saw the figure attack Victor's Clan body guard before going for Omi. Isis took her letter opener and stabbed the assassin, who then struck at Isis before escaping. This saved Omi Kurita, and a grateful Victor told her he owed her a favor for the act. Along with Omi, he sent Isis to Luthien to protect both women from further attacks. Unfortunately, in 3064 Isis found her friend dead, at the hands of the same assassin.
She then traveled to Muphrid in 3066, to see Victor again and collect on the favor he owed her - a dinner. Victor, still in shock from the death of his lover Omi, was shaken by stern talk from Isis on what was important and the need to move on. Victor, realizing he had been letting a great many people down, revived and resumed the war. Isis accompanied him in the last wave of the FedCom Civil War, all the way to New Avalon. In their travels, a relationship developed between the two, and they eventually decided to marry.
- Handbook: House Marik, p. 53 - "Isis Marik: Little Girl" lost - Isis Marik's mom is minor functionary.
- Handbook: House Marik, p. 52 - "The Coming of the Clans & Eagle Rising article" - Captain-General Thomas Marik creates an alliance with House Liao, using Isis Marik as the link.
- The Art of War, p.??