Stefan takes drastic measures to find out the real reason Katherine has returned to Mystic Falls, and is shocked when she reveals new secrets about what really happened in 1864. Damon tries a new tactic to resolve his issues with Mason (recurring guest star TAYLOR KINNEY), but it proves costly. Meanwhile, Tyler pushes Mason to tell him the truth about the Lockwoods, and when Katherine delivers an ultimatum, Stefan and Elena are left with very few options.