Showdown is the nineteenth book in the Sweet Valley High series. This focuses on Jessica and her on-again-off again feud with Lila Fowler.

A mysterious young man named Jack is introduced at a pool party at Lila's mansion, and Jessica is enthralled by him, and, as was the case for Jessica when she sees a handsome boy, she sees anyone as competition.  And in this case, it's Lila who is competition. Jack, unbeknownst to both Lila and Jessica, dates both girls.  He dates Jessica during the week, and Lila on the weekends.  However, Jessica resents the fact of seeing Lila's happy face on Monday mornings.  So, she schemes to remove Lila out of Jack's life, so she could date him exclusively. 

However, Jack was revealed to be a disturbed young man, who nearly tried to kill Jessica.  It took Elizabeth's friend, Nicholas Morrow and his friend, David, to rescue her.  Jessica then presses charges against the young man.  Eventually, Lila and Jessica reconcile and are friends again.