The Pines family is starting to get everything back to normal after the Lil' Gideon incident. They throw a “Mystery Shack Is Back” party, but some unwelcome guests intend to crash it.

Pacifica enlists Dipper’s help to rid the Northwest Mansion of a ghost before he wreaks havoc on her fancy party.

After agents Powers and Trigger take Stan into custody, Dipper and Mabel begin to wonder how much they actually know about their Grunkle Stan.

Cornered underneath the Mystery Shack, Stan must finally reveal the secrets of his past and his mysterious portal to Dipper and Mabel.