"Pretty Little Liars" season 6 officially returns Tuesday night. The hit mystery thriller comes back with a whole host of new secrets, big and small, and a brand new big bad who will remind liars that A is not the worst person they have come across.

When the girls reunite after five long years -– lives changed, some relationships thrived and some were outlasted -– each of them is keeping secrets from one another, something that Troian Bellisario aka Spencer is thrilled about.

"So the really exciting thing is to get to watch who these people are now, and how they interact now that five years have gone by — and a lot of stuff has happened in those five years," the actress told Entertainment Tonight of the girls' situation come "Pretty Little Liars" season 6.

When the show goes back on air, the girls will be all grown up. In the "5 Years Forward" special episode, Aria, Spencer, Emily, Alison and Hanna all turned 21. This prospect, which is definitely something new to the cast, especially excites the stars.

"It's nice to have mature conversations out of a high school setting," Ashley Benson aka Hanna said in the same ET interview. Shay Mitchell, who plays Emily, is just delighted to "be able to act like we do outside of the set, which is a little bit more mature, a little bit older, a little bit wiser."

Meanwhile, Lucy Hale promises that the friendship of the girls will remain the "heart" of "Pretty Little Liars" season 6. Although almost everything has changed, the actress, who plays the role of Aria, guarantees that the girls still love and support each other the way they did five years back.

"Pretty Little Liars" season 6 will resume on Jan. 12 at 8 p.m. ET on Freeform with an episode titled "Of Late I Think of Rosewood." Watch a livestream of the winter premiere on ABC Go.