How to unlock: you will receive this quest from Dr Carrington in Railroad HQ (M6,2) after you complete Railroad's main story (The Nuclear Option quest)
The quest is repeatable. During it you must reach selected random location and find one of the synths there. It will be a third generation synths, which means it will look like a human and will be wearing Institute's white clothes.
You must reach them and talk with them in order to give them information about a location to which they must go to be safe. You don't need to kill enemies in the location. Once you give the quest item to the synth, go back to Dr Carrington to receive the reward.
Quest rewards: 100-300 bottlecaps, occasionally a random weapon/armor part