Characters

Special Investigations: 2nd Unit

 * Joseph Morgan as Nick Michaels, the founder of 2nd unit.
 * Candice Accola as Lindsey Morgan, the newest and first female member of 2nd unit
 * Paul Wesley as Stefan Monroe, the head of 2nd unit.
 * Tyler Hoechlin as Derek Hale
 * Tyler Posey as Scott McCall
 * Dylan O'Brien as Stiles Stilinski
 * Shelley Hennig as Anna Johnson, a detective who joins in season 2.

Special Investigations: 3rd Unit

 * Ian Somerhalder as Damon Kelly, the head of 3rd unit.
 * Crystal Reed as Allison Argent
 * Nina Dobrev as Katherine Jones
 * Daniel Sharman as Isaac Lahey, a detective who joins in season 2.

Other

 * Holland Roden as Lydia Martin, a forensic analyst.
 * Taylor Spreitler as Tori Lancaster, an orphan girl.

Characters
Main Cast
 * Candice Accola as Detective Valerie Morgan
 * Joseph Morgan as Nick Michaels
 * Paul Wesley as Detective Stefan Monroe
 * Tyler Hoechlin as Detective Derek Hale
 * Tyler Posey as Detective Scott McCall
 * Dylan O'Brien as Detective Stiles Stilinski
 * Ian Somerhalder as Detective Damon Kelly
 * Crystal Reed as Detective Allison Argent
 * Nina Dobrev as Detective Katherine Jones
 * Holland Roden as Lydia Martin
 * Shelley Hennig as Anna Johnson (season 3-present, recurring season 2)
 * Daniel Sharman as Isaac Lahey (season 4-6, recurring season 2-3)
 * Taylor Spreitler as Tori Lancaster (season 6-present, recurring season 4-5) 

Recurring Cast

 * Phoebe Tonkin as Hayley Marshall
 * Steven R. McQueen as Jeremy Gilbert
 * Annie Clark as Meredith Bay
 * Claire Holt as Rebekah Michaels
 * Liz Gillies as Danielle Austins (season 4)