After watching the first half of tonight's Pretty Little Liars, I was a little worried that the show would fall into its old habit of slowing down the momentum and using needless filler episodes.

Fortunately, the second half really came through.

Pretty Little Liars Season 4 Episode 17 set the right tone for the continuing mysteries of the season and the series overall. We moved away from questioning Ali's motives and returned to finding out who killed Alison, who is A and whether or not those two are the same people.

Those aren't going to be easy questions to answer, and I'm sure we won't get those answers any time soon. But instead of stalling us with an ever-widening and complex tapestry of new characters and secrets (as it's done in the past), the drama has been really focused on just a few suspicious characters, helping us examine their motives and opportunities much more closely.

Watch Pretty Little Liars Season 4 Episode 17 Online

Hanna has been focusing her energy on solving the mystery of A by reading crime novels.

It seems like it's giving her good ideas, despite the fact that her friends are still intent on insulting her intelligence. Her dentist plan was a solid one, but somehow A found out. Cause A always finds out! That scene in the dentist's office was particularly terrifying. I already hate the dentist enough without having to be afraid of being gassed and tortured by a hooded figure.

Hanna wasn't the only one terrorized by A tonight. I'm still wondering what the purpose was for turning Emily into a paranoid basket case, unless A knew about her father's heart condition. That seems a little convoluted, but stranger things have happened.

Spencer, who is definitely not backing off anytime soon, plunged headfirst into the Board Shorts mystery, even using Andrew's "study aids" to stay up all night to decipher Ali's handwriting.

By the end, she looked way more disheveled than she did when she was in Radley. However, she may have stumbled on the biggest piece of evidence ever. Too bad it's going to be very difficult to get anyone (Aria) to believe her!

I am still loving the way the EzrA reveal has changed the dynamics of his character. He used to be just another dull love interest, but now when he speaks, all of his words and facial expressions take on multiple meanings. It adds a lot more depth to the scenes, and Ian Harding is doing a brilliant job with it.

So now Spencer knows that Ezra likes boysenberry pie and beer too? Seems a little too coincidental. Plus, the name of the beer he orders is Board Shorts Ale. And the conversation between Alison and her older boyfriend about her stories sounded exactly like the ones he and Aria had early on in their relationship. He did seem to run out of that pub pretty quickly after Spencer arrived.

All of this little things added up to a big problem for Spencer. Normally, she would just pursue this, but after what happened with Emily, I'm think she'll probably proceed with caution.

Or is this just another tactic to further separate the group? I still think there's another player involved because the A who terrorized Hanna and Emily was still hooded and shrouded in mystery. What for? The writers seem to be holding back to build to another big A reveal.

Is Mona helping Ezra out? If so, how long have they been working together? She's getting close to Aria's brother, but maybe we shouldn't be so quick to call her evil. Check out the Pretty Little Liars Round Table and offer up your own opinion.

Is Mona the devil?