That Sinking Feeling

That Sinking Feeling is a quest in the Fallout 76 add-on Wild Appalachia.

Quick walkthrough
Involves finding the following holotapes/notes:
 * A new day
 * C.H. Monthly, January
 * Day 1
 * Day 82
 * Letter to L

Detailed walkthrough
Start the quest by finding and reading a copy of C.H. Monthly, January. A copy is located at the Southern Belle Motel, on an outdoors table. Another copy can be found in Point Pleasant on the third floor of the barber shop near the edge of town.

Find Scoot's shack which is located somewhere south of the motel. It will be marked on the map.

After reaching Scoot's shack, access his terminal to find out where he went. Accessing his private research will require a password. The password is MA-RI-11-17.
 * The clue to the password is in Letter to L which is sitting next to the terminal. Scoot's cat "Mari" has the key to his heart and Mari's birthday as listed in the terminal entry 'Birthday Present Ideas' is 11/17.

Read Scoot's sheepsquatch research and find out that he most recently went to investigate a sunken church east of Haven Church. Travel to the area marked on the map and search for the sunken church.

Enter the church and search for clues as to what happened to Scoot:
 * Day 1 - Note, on the ground at the start of the tunnel beneath the church building.
 * Day 82 - Note, on the ground near some church windows in the sunken building.
 * A new day - Note, on an altar in the sunken building.

Kill the wendigo which spawns to complete the quest.