The Secret of Cabot House

The Secret of Cabot House is a side quest in Fallout 4.

Detailed walkthrough
When returning to the Cabot House after saving Jack's sister, the Sole Survivor will get this mission assigned by Jack to help prevent raiders from freeing Lorenzo. Although one can actually fail in preventing the raiders from freeing Lorenzo, the Sole Survivor still has to kill them all once Lorenzo is released. Use the elevator in the control room to return to Cabot's office.

Plan A: Kill Lorenzo

 * 1) Upon flipping the switches and killing Lorenzo, Jack states Lorenzo would have killed his family as well as the player. He says his family influence was the only thing keeping his father in the asylum as opposed to death row due to his crimes during his life. Jack says that now that the world is "built for monsters," nothing would have stopped his father from presumably returning to criminal activity. One can choose to thank him, or berate him for being sad only because he "lost [his] immortality juice;" though Jack seems to genuinely believe he could have removed the artifact and cured his father with a little more research. He awards the player with about 500 caps and tells them to return to his home in about a week. He gives a slightly different amount of caps depending on what the player says after killing his father.
 * 2) When an in-game week has passed, there will be a notification that says to visit Jack back at the asylum. He tells the player character he figured out how to access the telekinesis effect of the artifact. He gives the player character Lorenzo's Artifact gun.

Plan B: Free Lorenzo
Choosing to save Lorenzo by pushing the switch by his door will prompt Lorenzo to leave his cell; him saying he wants to have a "long overdue" conversation with his son. He tells the player character "we'll have to kill him, you know. And the rest of them." He says his son trapped him in there in 1898; nearly 400 years before the in-game date.
 * 1) Arriving at Cabot House, Jack will ask why the player freed him. The next conversation options will allow one to either help Jack further by saying the player character can help him, or help Lorenzo by saying he is wrong and then killing the Cabots. Whatever one chooses to say, Lorenzo will appear on the balcony overlooking the family room. Wilhelmina tries to sell Jack out by saying she would never allow him to do what he did, but Lorenzo berates the family for feeding on his blood. Lorenzo then turns hostile to the Cabots (and the Sole Survivor if decided to help Jack).
 * 2) After killing him, Jack will award the player 502 caps, saying he no longer needs their services. Every quote from him following the quest's end will be he either mourns his lost family or berates the player for not listening to him.
 * 3) (If successful in keeping every family member alive, asking for more rewards allows one to come back in a week to receive Lorenzo's Artifact gun. However, if the player waits one additional week before returning to Cabot House, Jack ages and Wilhelmina Cabot dies due to lack of access to the serum. The quest marker "Talk to Jack Cabot about the artifact" now points to a spot in the kitchen and cannot be completed.)
 * 4) Otherwise, after killing the Cabot family, Lorenzo will offer a "lifetime supply" of mysterious serum, albeit one at a time, which cannot be sold or traded away.

Plan C: Take Both Actions
The following describes the details for Plan C in which one frees Lorenzo and then kills him before he leaves the area that is outside his cell:
 * 1) One can activate up to 3 switches and still open the door of Lorenzo's cell to let him out.
 * 2) Once he is out, one can speak with him to find out what he intends to do.
 * 3) Then he can be engaged and killed easily.
 * 4) Return back to Cabot House and Jack will be upset that the Sole Survivor set Lorenzo free, but the Sole Survivor can tell him that they killed Lorenzo and that they are sorry that they did so. Jack will give them 500 (or so) caps.
 * 5) After a week the player can return and Jack will give them Lorenzo's Artifact gun. It is possible to wait too long and make the weapon impossible to obtain.