"Pretty Little Liars" season 6 episode 6 is titled "No Stone Unturned" and it will mirror the girls' determination to find out who their tormentor was. Interestingly, the Liars stumble upon a discovery that makes them believe that there's more to Mona's friend Lesli than meets the eye. 

Lesli was furious at Mona for ruining her life ever since she helped her fake her death. She was introduced in season 5 after Mona's plan was set in motion. Lesli became a person of interest when it was confirmed that she was a Radley Sanitarium patient, too.

That means that she stayed in the sanitarium at about the same time Charles DiLaurentis, Mona and Bethany Young were admitted there. She was in the same room with Bethany, who was mistaken for Alison at one point.

This sends the girls springing into action in "Pretty Little Liars" episode 6.

Before bringing it up to the police, however, Hanna and the group search for "concrete proof" that Lesli is indeed "A," their tormentor. However, whoever "A" is, he or she is one step ahead of them. In the trailer for the episode, it is revealed that "A" managed to put a tracking device on the ladies. 

Finding more about "A" is like digging their own grave. In the synopsis for the episode, "A's threats escalate" as the girls continue to investigate, so it looks like the baddie is nowhere near done toying with the girls. 

As the girls find more answers about "A's" identity, more mysteries seem to come about. In an Instagram post, executive producer Marlene King said that the red hood's final appearance will happen in the finale of the season. 

"Pretty Little Liars" season 6 episode 6 "No Stone Unturned" airs on July 14.