From Halopedia, the Halo wiki
Walkthrough: During the level Composer, outside the station. The Terminal is located within a cluster of rocks under the Atrium.
Flood-infested ships hover above a planet as the Mantle's Approach drops out of slipspace. A door on the bottom of the Mantle's Approach opens and multiple Knights fly out to attack the infested ships. A Knight lands on one of the ships and cuts an entrance into the ship, allowing it to go inside. Soon thereafter, the ship, along with two others explode from the inside. The Didact watches from his flagship.
He looks at a holographic representation of a Halo installation. On its surface, the humans go about their daily activities.
The Mantle's Approach hovers over the human village.
The Composer activates, digitizing everyone in the village. Cut to black and then fade in to show the ashes of the human remains touching the Librarian's hand.
Two Lifeworkers survey the area where the humans were digitized. The Librarian turns to face the holographic representation of the Didact.
On the surface of Requiem, the Didact is talking to the holographic representation of the Librarian while he is surrounded by Knights.
Cut to black and then fade in back to the Librarian.
The Librarian proceeds to walk away.