1. John finds Cortana (now rampant free due to Forerunner technology)
2. John and his team of Spartan II's (Linda, Kelly, Fred, etc.) proceed to rescue Dr. Halsey
3. They then use the Janus Key to discover the Forerunner Technology, specifically the Forerunner Base of Operations
4. They proceed on a mission to this HQ
5. There they discover the Ur-Didact fighting against the original (non-flood form) Pre-Cursors
6. The Ur-Didact perishes while fighting against this new enemy, but not without handing over control of his Prometheans to John in order to defeat the Pre-cursors. In the end, the Ur-Didact has given up his anger and helped humanity attain the mantle--the endeavor, which his wife--the Librarian--always desired him to pursue
Halo 6: Humanity Leading the Galaxy (Mantle) Against the Pre-Cursor Threat