Unsolved: Picnic Panic is a quest in Fallout 76. It was introduced in Patch 8 in April as part of Wild Appalachia series of content.
Synopsis
Before the war, two girls went missing from Clarksburg. Dwellers can commit to picking up the investigation decades later to see if they can determine what happened to them.
Walkthrough
The picnic site is located north of the Woods Estate and south of the Willard corporate housing park. The site is easily recognizable by the bicycles. To solve the mystery, players need to find the following clues:
The two bicycles, which provide an address for the Wesley's home in Clarksburg.
Players then have to head over to Clarksburg and look for the Wesley's home. It's just northwest of the Shooting Club. The clues there are the cow magnet and loaded dice by the back door and Chelsea's Diary Page.
The next stop is Mary Tinley's home, located to the northwest of Clarksburg, inside a half-submerged trailer. The clue here is in the backback (best searched after dispatching the ghoulified remains of Mary's father, Harvey Tinley). It's Mary's Diary Page. Completing it completes the quest.
In the end, this is a tragic tale. Chelsea came from money, but Mary's family were poor. Despite coming from different worlds, they became friends. Chelsea would regularly cheat at all their games, refusing to believe that a girl like Mary could be allowed to win. Mary confronted her and Chelsea must have revealed her true, elitist feelings. Mary snapped and drowned Chelsea and then took her own life with rat poison.