The Master Builder and someone else decided to build the Halos and each of the Halos has a powerful, energy weapon that can destroy a whole life-form with enough biomass to sustain The Flood in an whole star system.
Born learns that Halo was test-fired on the human worlds that Born visited and Master Builder test-fired with another Halo on San'Shyuum's homeworld.
The Forerunner Council found out about Master Builder's actions and Born was summoned to a criminal trial against him.
High above the Forerunner world sat 11 Halo rings, one was missing for many years. The trial was interrupted by Mendicant Bias and a rampant AI, who caused destruction with the Forerunners.
Plot Con.
Didact took Born and humans to the San'Shyuum's world where they lived since the Human-Forerunner War ended.
The four were caught by the Master Builder and Born got sent home to his family, during his trip home the Didact's memory tells him that Halo was the reason that Didact was placed in the Cryptum.
Didact wanted to prevent the creation of the save-haven "Shield Worlds.
Born overheard his dad argue with the Forerunner Council and he confronts his dad and tells him about the Halos and that The Flood is reappearing in their part of the galaxy, and the Forerunner lost to them 300 years ago.
Plot Con.
The four went to series of worlds that was battlegrounds in the Forerunner-Human War. When they went to those worlds, the worlds didn't show any feeling or complex life to Didact's dismay.
He ask Born to take a brevit mutation to have some traits of the Warrior-Servant caste. Those traits let Born to see Didact's memories and his class, when Born accepts Didact's ofter he saw the memories and learns that Didact regretted the war with the humans.
There was two wars that the humans were fighting and the third race was "The Flood". The Flood is a galactic threat and it infects a body and make mutate and they're not alive like a zombie and they become aggressive.
The humans won against The Flood by injected a toxic that hurts The Flood, the humans didn't tell the Forerunners how to beat The Flood when they came back.
Plot
The story starts out with three characters and their names are Chakas, Riser, Bornstellar Makes Eternal Lasting (Born) on a ship.
They are traveling through a sea with creatures and while they are on the ship, Born takes off his armor.
Born was builder for the Forerunner race but he changed to become a hunter to find Forerunner and Precursor lost artifacts. Born finds a Forerunner Cryptum, it is a vault that Forerunners are in never ending sleep.
When Born was in the Cryptum he sees a monitor looking over the Cryptum, he wakes up a Forerunner who was sleeping and the guy was a member of the Warrior-Servant caste.
Ur-Didat was the forerunner who woke up and he thought that Born and the humans that the Librarian sent to wake him up and takes them to ships to retrace his steps to being put in the Cryptum.
He was desperate to see if the Halo Array was fired.