Isaias Sandoval is first encountered after Adam Jensen returns from the Highland Park FEMA facility, where he, along with Bill Taggart, is at Sarif Industries. There Jensen can inquire about him, where he reveals he has a particular hatred for augmentations, having spent much of his career helping out victims of implant rejection and Neuropozyne addiction, and witnessed the dangerous side effects firsthand.
He reveals he had a brother who was an augmented veteran. This brother suffered augmentation psychosis as an effect of his military-given implant, and attempted to commit suicide-by-cop by going on a rampage at a shopping mall. However, he was successfully talked down with no deaths by Bill Taggart, who treated him. Because of this incident, Sandoval feels he has a personal debt to Taggart.
Later, Jensen finds out from Eliza Cassan that Sandoval was personally involved in the attack on Sarif Industries, having assisted the Tyrants by surgically removing the Sarif scientists' GPL implants so they could be kidnapped. It turns out that Sandoval could not entirely remove all of the implants; he could only lower the frequency to a point that no one would know to look for. Jensen obtains Sandoval's location from Taggart - a rundown apartment in Detroit near Derelict Row. However, when he reaches the apartment, he finds it is actually the entrance to a secret underground bunker and hiding place of Sandoval, filled with Purity First members, an organization Sandoval had secretly been assisting behind Taggart's back all along, knowing his disdain for violence.
Jensen finally confronts Sandoval in his private office, where he loads up a revolver with a single round and prepares to kill himself. Knowing his secret is out and his career is over and that Taggart now will work to distance himself from him, Sandoval fears he has no future but in prison and thinks of himself as a mass murderer for his complicity in the Tyrants' activities, and is prepared to take his own life. However, Jensen can talk him down with some persuasion, and Sandoval will agree to being arrested peacefully. Here are the responses for the peacefully win: Sandoval says "he'll just spin it again" = tough love or empathize. If he says help "help pro-augmentation" = tough love. If he says "I was an idiot" = inspire. If he says "look my wife in the eyes" = empathize. If he says "am I the only person who fells this way" = empathize. This list may be incomplete.
Alternatively, Sandoval will die by suicide if Jensen chooses to Inspire, then Inspire again, then (if Sandoval is still alive) Empathize. Conversations do not always follow exactly the same script. Sandoval may die before Jensen has the chance to make his third dialogue choice.
If Sandoval does turn the gun on himself, Jensen will look away as the trigger is pulled. However, an exit wound appears on the back of Sandoval's head after the cutscene is over.
If Sandoval is kept alive, he will give Jensen some information regarding the Tyrants and their attack on Sarif Industries, particularly that the scientists, including Megan, were taken alive.
However, in the special case when Jensen gets the information regarding Sandoval's location without publicly confronting Taggart, a different cutscene is triggered; Jensen bursts into Sandoval's office as he attempts to contact help, disarming him and demanding the location of Sarif's kidnapped scientists. After Sandoval reveals what he knows, Jensen suffers a glitch that allows the former to reclaim his revolver and attack him. This forces Jensen to either kill him or knock him out.
Other that they approached Sandoval thorugh his brother Ezekiel, it is never fully explained why the Tyrants turned to Sandoval for assistance. During Jensen's confrontation, Sandoval angrily states that "Taggart already knows the truth", suggesting that Taggart was truly cooperating with the Tyrants during the attack on Sarif Industries, providing them with Sandoval's expertise as a physician. This is further supported by a pocket secretary found in the FEMA camp's infirmary, in which Taggart tells Sandoval that his expertise as a surgeon kept the captured scientists alive.
The following is the CASIE Social Enhancer's summary of Isaias Sandoval:
- Desperately needs someone who can unearth the good in him.
- Can easily fall into a gloom state from which he needs to be elevated.
- Tends to rationalize events so he doesn't have to deal with them. Forcing him to get through is the only answer.
- Isaias Sandoval is left-handed.
- Despite him only visibly loading his revolver with one bullet, the revolver can be picked up for five rounds.
- Hacking anything or going backstage before engaging in conversation with Taggart at the convention center will cause Sandoval to be hostile, preventing the conversation and forcing Jensen to kill or knock out Sandoval, and keeping the "The Last Straw" achievement from unlocking.
- Isaiah and Ezekiel are the names of prophets featured in Judaism and Christianity.
- Sandoval is an omega type personality.
- His blood type is O Negative.
- It is possible to accidentally "lock" the mission path into Sandoval being hostile (instead of suicidal). Although it has been speculated that this was due to hacking Taggart's computer, it can be triggered from a variety of causes, and some players have reported success through using the computer and planting evidence. It is NOT required to start a new game to avoid this once it occurs, as was previously supposed, rather it is possible to be resolved by loading a save at or around the very start of the Detroit 2 area, and proceeding with the main quest immediately without completing any side quests. If proceeding along the path of conversation with Taggart to reveal Sandoval's location, it is necessary to avoid any hostile action within the convention center whatsoever, including hacking alarm panels or the security computer.