Alison is back on Pretty Little Liars.

So... now what?!?

For Spencer, the most important mission on Pretty Little Liars Season 4 Episode 17 ("Bite Your Tongue") will be to get to the bottom of Ali's diary. It must contain clues to her real agenda, right?

But they will take awhile to figure out. Like all night, every night. This means Spencer's will need some help from Andrew, as teased in the following clip. Help that comes with a child-proof cap...

Elsewhere, Aria and Mona will have it out, with the latter making some salient points and sort of putting the former in her place.

Watch the pair square off now:

Did you catch the previous installment? Need to relive any of the show's most recent moments? Sit back and watch Pretty Little Liars online right now!

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.