(s04e05 “Employee Transfer”)

Official episode description

“Employee Transfer.”
Pam (Jenna Fischer) is embarrassed when she is the only person at corporate wearing a costume on Halloween. Holly (guest star Amy Ryan) and Michael (Golden Globe winner Steve Carell) take the long trip to Nashua after they get some shocking news from corporate. Meanwhile, Dwight (Rainn Wilson) torments Andy (Ed Helms) and tries to get under his skin.