Zero Hour

Zero Hour is a secret quest found on Earth when the player has the Fallen Transponder and has activated all 6 of its nodes. A completion of this quest awards the player with the Outbreak Perfected Exotic Pulse rifle. This quest can be accessed via the Earth directory or by interacting with Mithrax, the Forsaken in The Farm basement after the player has the Fallen Transponder and has activated all 6 of its nodes.

Heroic version
After the completion of the quest, a heroic version will be available via an option after selecting the Zero Hour mission on the Earth directory. When the player completes the heroic version of Zero Hour for the first time, they will be awarded the Outbreak Perfected Exotic catalyst. After the player completes the heroic version of Zero Hour for the first time, further completions will award 100 SIVA Nanites which count towards completing the Outbreak Perfected Exotic catalyst.

Obtaining the Fallen Transponder and activating the nodes
In order to start this quest, there will be a heroic Adventure that will have to be active in order to start this quest, after proceeding through the quest there'll be a shrieker that will need to be killed, after killing it, make a left in the room behind it (The room will have a red tint to it) There will be a door with a prompt that reads "Unlocked" when you kill the shrieker. Interact with the door then proceed through the room and there will be a red node right next to a table, interact with the node and the player will obtain the Fallen Transponder. The Fallen Transponder requires the player to collect six nodes in order to make progress. Four of the nodes are located on Earth and the other 2 nodes are located on Nessus. All of the nodes will be in lost sectors. After collecting all the nodes, go to The Farm and take a right from the spawn point toward a cellar right next to the hangar and go down the stairs, at the very bottom, Mithrax, the Forsaken will be crouched down at the end of a hallway, and then the actual quest will begin.

Trivia

 * The path players take through the beginning of the mission is largely the opposite from the Homecoming mission.
 * Mithrax only aids you once at the very beginning of the mission and isn't seen again until the very end.
 * Though enemies of the mission are loyal to Eramis, a Fallen Baroness seeking to reestablish the House of Devils, all enemies encountered have the colors of the House of Dusk.