Unlikely Valentine

Unlikely Valentine is a main story quest and achievement/trophy in Fallout 4.

Detailed walkthrough
After speaking to Ellie Perkins, it is revealed that Nick Valentine is being held captive in Park Street station. The station is filled with Triggermen, but inside the station is the entrance to Vault 114.

The vault is guarded by Triggermen armed with submachine guns, 10mm pistols, and at higher levels, .44 pistols. The Sole Survivor needs to fight their way through the vault until they come to a large open atrium. Guarding the overseer's office, where Nick is being held, is a Triggerman named Dino. Sneaking close allows the player character to listen to the conversation between the two of them where Valentine convinces Dino that a crime boss is upset at him about his cheating habit during gambling. Dino then runs out of the room to square things off with said crime boss, leaving the coast clear to free Valentine. Alternatively, Dino may be killed without waiting for him to leave. The control panel next to the office door can then be used to free Valentine.

Speaking with Nick reveals why he is there and that they should leave as soon as possible. On the desk behind him is the speech bobblehead. After talking with Nick, he will take the lead out of the vault where Skinny Malone and Darla will be waiting to stop the escape. With a few speech checks it is possible to turn them against each other or leave the vault without fighting at all. If a certain stage of the unmarked quest, The Sight has been completed before coming to the vault, there will be an additional speech option that allows escape without any violence and Darla will depart also, as Skinny Malone will advise they have 10 seconds to leave. Otherwise, the Sole Survivor and Valentine will need to kill Skinny Malone and his companions in order to leave.

After exiting the vault there is a short conversation with Valentine where he directs the Sole Survivor to meet him back at his office in Diamond City. Upon arrival, speaking with Ellie will end the quest.

Behind the scenes
The premise for Nick being in the vault is similar to the story from the film The Big Lebowski, in which a private detective is hired to track down a family daughter-turned-crime boss' trophy wife.

Bugs

 * When confronted by Skinny Malone and Darla, the accompanying Triggermen will become hostile if a targeting helmet is worn. Removing it will suffice. The highlight ability from Berry Mentats seems to make them hostile as well.
 * Nick will turn hostile and shoot Skinny Malone and Darla but will not shoot the Triggermen.
 * After killing Skinny Malone, Nick Valentine will stand by the door and be unable to follow the player.

Sei mein Valentine Un Valentín muy poco santo Detektyw o stalowym sercu Não é Bem São Valentim Валентайнов день Валентайнів день 怪客瓦倫坦