Valentine's Detective Agency Radio is a radio station in the Fallout 4 add-on Far Harbor. It can be picked up after installing the add-on, provided Nick has already been rescued from Park Street station.
The radio signal is available after completing the quest Getting a Clue and must be listened to to progress with the Far Harbor quest Far from Home. Upon listening to the radio Ellie Perkins will tell the Sole Survivor to return to Valentine Detective Agency in Diamond City as she has a new detective case that requires urgent attention.
This is Ellie Perkins from Valentine Detective Agency, with a message for Nick's partner. We got a new case and it sounds urgent. Stop by the office, I'll be waiting.
Setting this to repeat.