The Voice of Set is the Mistress of Mystery's iconic gun. To earn their own, the dweller needs to recover data from an experimental weapons research program.
Cryptos' briefing gives the destination: Sugar Grove, the black site on the other side of the mountains. The goal lies within the facility's SigInt section, namely the research division. After finding through the robots, the player has to interact with the terminal surrounded by blank tapes to learn of the EMP weapon project - and the woes of the researcher in the logs, who accidentally filled the entire storage volume with test data.
To contain the data without having to lug a mainframe into the Grove, the player has to obtain the Project Siphon Holotape. To learn about this, they first need to read the last of the researcher's logs, then acquire it from from the analyst's terminal. While the waypoint can break, the terminal works as intended. The analyst's terminal is in the corridor leading away from the security checkpoint before the main SigInt chamber: First door on the left. Once accessed, the player simply has to dispense the holotape, then play it on the advanced research terminal to gather the data.
Finally, the player has to return to the Riverside Manor and play the holotape at the fabricator. Cryptos will make sense of the data and allow the player to fabricate the Voice of Set.