Alad V sends you a message, and then you unlock mission nodes in sequence on Mercury, Venus, Earth, and Jupiter. After you complete these missions, the Acolytes will spawn on specific missions for a short period of time. You can view their health and location on the navigation screen on the second tab over. These Acolytes leave after you die or inflict enough damage on them. If they leave for the second reason, then they drop event-specific mods. The Warframe community has to band together and kill them all to unlock the last part of Operation: Shadow Debt. There are currently 6 days left for us to finish them off. There are a total of 6 Acolytes, and they show up in a group of 3. Once one of these 3 is killed, the 4th and 5th replace them. Once they're all dead, you will unlock the last mission of the event. At the completion of this event, you will earn a new version of the Vulkar sniper rifle as a reward.