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Pretty Little Liars episode
Episode no. Season 1
Episode 1
Original air date June 8, 2010
Guest characters
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List of Pretty Little Liars episodes
Pretty Little Liars (season 1)

"One Big Mistake" is the series premiere of the mystery drama series Pretty Little Liars. It introduces each of the main characters, as well as establishes the basic premises of the series. The episode aired on June 8, 2010 on ABC Family.


  • Alison DiLaurentis (main)
  • Spencer Hastings
  • Aria Montgomery
  • Emily Fields
  • Hanna Marin
  • Mona Vanderwaal
  • Mike Montgomery
  • Jessica DiLaurentis
  • Veronica Hastings
  • Peter Hastings
  • Ashley Marin
  • Ella Montgomery
  • Bryon Montgomery
  • Pam Fields


Alison DiLaurentis, a typical queen bee, decides to pull off something big to start off 10th grade with a bang; however, this plan does not go as she planned it. In result of the aftermath, Alison decides to keep this life-threatening mistake to herself; thus keeping her friends in the dark. At the end of the episode, Alison is seen fleeing town with false identification.