Cold Case

Cold Case is a side quest in Fallout 76.

Detailed walkthrough
Before starting this quest, note that the level of the unique weapon Perfect Storm will vary with the current level of the player character at the time of quest completion. Because this is the only chance this weapon can be obtained, it may be desirable to defer completing this quest until reaching level 50.

The quest starts after encountering a robotic nanny, Miss Annie, at Wavy Willard's Water Park, who is concerned about a child, Freddy, who disappeared while the robot took him to this amusement park. She asks the Vault Dweller from Vault 76 to check the security holotapes.

The Park Security System is inside the ruins of a building. Access the machine and check the Holotape Review - the text talks about a missing kid. October 23 mentions a tape. Reading this will update the mission. The next step is to locate and play two holotape clues. One is nearby, the other is a bit harder to find but the entrance to it is in the next building to the north. Go inside the fence at the back of the building and look for a staircase down. The tape is in the basement on a bookshelf.

Look inside the mailbox outside of the same building as the second tape, through the fence on the right. The letter to the media will be inside and pop up on the screen when looted. The note mentions a key. The next waypoint is at the top of a waterslide tower on a box. This leads to a KidSecure ID that was made for Freddy Wood.

Go to Clarksburg and locate the Post Office. The mission will update when the player is close. Use the terminal inside to research the key. Search by box number and read the entry for thirteen. The next step is in Otis Pike's house, some distance to the northeast. Inside the house is another terminal. Use it and read Correspondence/Dam Safety Inquiry.

Gain access to the Grafton Dam building to complete the next step. Both doors are locked, but there is a hole in the wall. Super mutants guard the dam, and expect a run-in with Mad Dog Malone if Manhunt is active when heading to the dam. Search for clues inside the dam, and make sure to find the keys so it is easier to access the dam later without needing to pick the door locks without the keys.

After reaching the Woods Estate, go upstairs to find a desk with a terminal. Loot the note in the desk to progress the mission. The terminal has related information, but accessing it is not necessary to complete this checkpoint. Fast travel or walk back to Wavy Willard's Water Park and interact with Miss Annie to complete the quest. Completing the quest will earn the Perfect Storm, a 10mm submachine gun that fires incendiary rounds to burn the target for several seconds.

Bugs
Prior to patch 1.1.4.3., the optional quest to fix Freddie's KidSecure ID occasionally did not work even when the player character had the required materials in their inventory.