Unlikely Valentine

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

Synopsis
A detective who has mysteriously disappeared is the first big chance at finding the Sole Survivor's missing son. The Sole Survivor will need to track down the detective, starting from his last known location.

Walkthrough

 * 1) The Sole Survivor, with intel at hand from Valentine's secretary, will track down the missing detective through Park Street station.
 * 2) Traveling through the metro, the Sole Survivor will discover that the entire station has been taken over by a mob boss and his triggermen, with the trail of their corpses leading to a secret vault within the furthest end of the tunnels.
 * 3) It is discovered that this is Vault 114, and that the mob boss that has taken over, Skinny Malone, is holding Valentine hostage within.
 * 4) After fighting to Valentine, and releasing him, it is discovered that Valentine is a peaceful synth, and that the mob boss that captured him, was an old enemy that was keeping him alive for nostalgic purposes.
 * 5) During the escape, the group is confronted by Skinny Malone himself, alongside the girl that Valentine was tracking down, who is revealed to have run away from home to be the mob boss' girlfriend.
 * 6) At this point, the Sole Survivor may: kill Skinny Malone and everyone with him, convince Malone to let them go, or convince Malone that his newfound girlfriend is bad news, in which Malone will let Valentine go, albeit giving them until the count of 10 before he changes his mind.
 * 7) After escaping from the vault, Valentine will lead the Sole Survivor back to his agency, in which they can then discuss Shaun, which will open up Valentine as a permanent companion.