Lesli Stone will start on top of the Pretty Little Liars' 'A' list in season 6's sixth episode.

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Titled "No Stone Unturned," the search for Lesli will kick off following a visit from her sister in "She's No Angel." It seems the other Stone will set off some alarm bells when she journeys to Rosewood in order to berate Mona.

"With all signs pointing to Lesli as the tormentor in the hoodie, the PLLs are on a mission to get concrete proof before bringing their findings to the police," ABC Family teased. "But as the girls ramp up their investigation, "A's" threats escalate."

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'A' doesn't want to get caught, but it seems he/she isn't ready to throw in the towel.

What does the Lesli theory mean for Charles DiLaurentis? Is Alison's mysterious brother truly dead? Is Lesli someone Charles knew at Radley? Could the two be working in tandem?

Viewers will have the truth by time "Game Over, Charles" airs this summer but until then, theories will continue to fly.

Find out more when Pretty Little Liars airs Tuesdays at 8 p.m. ET on ABC Family. Click the video below to see a preview for the series' latest episode, "Don't Look Now."