They betrayed you, they tried to kill you, in some cases they really did kill you. But within the space of an episode or two, you find it in your heart to forgive them. As long as they're a fellow series regular. Usually an instance of Plug N Play Friends. If the unmasked traitor was an active party member or contributing part of the team, and remains an active party member or contributing part of the team, it's Welcome Back, Traitor. Examples of Easily Forgiven include: