Pretty_little_liars_3x06

: It also deepens the mystery surrounding Toby’s mother, Marion Cavanaugh, suggesting that the "accidents" at Radley were planned or covered up long in advance.

: This paper leads them to discover that a room was built into the sanitarium that wasn't on the official public records—a room that "A" (Mona) was using to sneak in and out of the facility. Pretty_little_liars_3x06

: Spencer realizes the blueprint is dated months before the construction of that wing actually began. : It also deepens the mystery surrounding Toby’s

: While searching through a box of Toby’s things at the Apple Rose Grille, the girls find a blueprint for the "East Wing" of Radley. : While searching through a box of Toby’s

In the Pretty Little Liars episode "The Remains of the 'A'" (Season 3, Episode 06), the "interesting paper" most likely refers to the found by Hanna and Spencer .

Here is why that specific piece of paper was so significant: