S5, E14: As Damon’s behavior escalates from destructive to deadly, Stefan begins to regret their last conversation and decides to track Damon down and intervene. For reasons of her own, Elena volunteers to come along. Dr. Wes (recurring guest star Rick Cosnett) enlists the Travelers to set a trap that will once again test Damon’s friendship with Enzo (recurring guest star Michael Malarkey). After a heart-to-heart talk with Nadia (recurring guest star Olga Fonda), Matt enlists Caroline and Tyler’s help to protect Elena, leading to a violent confrontation. Later, when Stefan tries to comfort a dejected Caroline, their conversation leads to a horrifying realization.