In Sheep's Clothing

In Sheep's Clothing is a quest in Fallout 4.

Quick walkthrough
This quest starts when the Sole Survivor reaches level 20 and travels to Diamond City after the main quest line. Mayor McDonough will be seen shooting a security guard before fleeing to his office, where he holds his secretary hostage while Piper attempts to apprehend him.

Detailed walkthrough

 * 1) Chase McDonough to his office. (Optional) Talk to a doctor and bring him to the wounded guard. You can also choose to use a Stimpack to heal him. If Curie is with you, she can be asked to take care of the guard, in which she will be happy to do so.
 * 2) Break into McDonough's office and confront him with Piper. You can either choose to lockpick the door, which is a novice lock, or use a button located underneath the secretary's desk.
 * 3) Decide how to deal with McDonough. Passing a medium difficulty speech check will convince him to release his hostage. He will then request that the Sole Survivor allow him to safely leave the city, giving him or her the option to comply, kill him on the spot, or make him stand trial, starting a fight.

Bugs

 * If McDonough shoots Geneva during the fight, she will become hostile to everyone. This causes Piper or any other NPC to kill her, worsening the player's relationship with Piper and occasionally turning her hostile towards the them.
 * A bug may occur where Piper and McDonough start shooting at each other after you open the door. The mayor cannot be talked to in this case. A workaround on the PC version is possible if you open up the console and temporarily disable Piper. The mayor can then be reasoned with or killed, and Piper can be re-enabled after the Mayor is gone or dead. Simply disabling combat or general AI will not work.