From Halopedia, the Halo wiki
Lord of Admirals
Walkthrough: In the level Forerunner, during the journey to the first pylon, the player will reach a symmetrical platform. After clearing the Prometheans in that area, John's HUD will be distorted, which prompts him to ask, "What's that distortion?" Under the door leading to the next area is the Terminal.
A Forerunner fleet orbits a Forerunner planet. A shuttle enters one of the planet's portals. The scene switches to a shot of many tall towers.
View of a large room with a holographic table in the middle. Lifeworkers float across the room, doing various tasks.
The Librarian turns to face the Didact.
A holographic image of the planet appears in front of him. He manipulates the image with his hands.
The image of the planet turns red in several places.
Flood biomass spreads across a Forerunner structure. The camera pans to the sky, and the scene rapidly flashes to white as the orbital bombardment begins.