Criminal Minds: Season 6, Episode 18

6 - 18: Lauren

As Prentiss faces off against her sworn enemy, Ian Doyle, the BAU call in JJ in the hope that she can help them find Prentiss and capture Doyle before it's too late. Although JJ later tells the team that Prentiss is dead, it's actually revealed that Prentiss is still alive and that she faked her own death before going into hiding with only JJ and Hotch knowing.