FLASHBACKS TO A DARK TIME IN DAMON’S LIFE - Stefan continues to offer Katherine his support while trying to mask his own pain, until Caroline shows up with an unusual form of therapy. After trying to make amends with Caroline, Elena grows so concerned about Damon that she turns to Aaron (guest star Shaun Sipos) for help. Later, when Damon tells Elena about a terrible ordeal in his past that he has kept secret for decades, she shares the disturbing information she just learned about her own family. Finally, Aaron decides on a desperate course of action after a conversation with Dr. Wes (guest star Rick Cosnett).
— OFFICIAL SYNOPSIS FOR THE VAMPIRE DIARIES: THE CELL (EP509)