John Van Druten, no less.
Hanna spends more time than ever wondering if Mona's really as serious about not being crazy as she's acting, but once Lucas tells her his A-Team secrets -- and then Mona deposes Spencer as the new Captain of Academic Decathlon, having sabotaged the reigning leader's bicycle last week -- Hanna unloads on the girl, possibly reactivating her craziness but almost certainly sealing Lucas's death warrant.
Lucas's involvement in this whole mad parade, we learn, started back during Masquerade Ball, when he was part of the Black Swan thing. Which it turns out was apparently just Mona making him and Melissa swarm Jenna so that she could kidnap Spencer without anybody noticing? I think. Anyway, he was not on the A-Team before then. And then when she was in Radley, he was pressed once more into service delivering messages to Mona from Jason DiLaurentis. (One of those clues that nobody seems to actually hear, as often happens on this show.) Anyway, he wanted out, and once Mona (he doesn't know about Toby) tried to run him over, he stopped selling test answers so she wouldn't have anything on him, and now he fears for his very life and wants to quit school.
So you can see why Hanna would lose it after hearing this, although mostly it's about her righteous anger at having worked so hard on being fair and compassionate with Mona, regardless of all the shit she's pulled, only to look like a total dingus. On the other hand, reactivating Mona's insanity by doing the exact same thing she explicitly explained drove her crazy in the first place is probably something that will end up having consequences, no matter how great it feels.
Aria gets Ella (Ella!) to spare some details on the night of Ali's murder: Apparently Byron got her so drunk she passed out, which is why no adults were available, but also opens up the possibility of him sneaking out to see and/or murder Meredith and/or Alison. Later, Meredith admits that he did come see her that night -- but not for a hookup. He thought she was involved in Ali's extortion attempts, and Meredith claims he left her place for his last meeting with Ali. In the current time frame, his freaky behavior causes Meredith to seemingly switch sides, and by episode's end she has committed to taking care of Aria while he's out of town so they can solve his part in the murder together.
Emily and Paige attempt to go to a swim team party, bravely fighting their battles against curfew and PTSD agoraphobia respectively. Eventually Paige has a total breakdown, revealing that she has gone a whole new kind of crazy in the wake of Masquerade Ball/Cousin Nate/Halloween Train, and is no longer able to leave her house. Emily, of course, couldn't love it more since she loves how crazy Paige is -- and then even gets to chase A-Toby around the woods for awhile, to get some of her aggression out. All in all, a nice couple days for Emily.
With Spencer questioning everything, from her own intelligence to the suspects in her million inquisitions, this victory from Mona just lays her low. Hanna's rising to the occasion in a Spencer way, but Spencer just wants everybody to calm down and stop letting Mona bait them all the time. It is a shocking reversal, to everyone involved. We'll see how long it lasts, though, because from where I'm standing Spencer is staring down the barrel of a total meltdown, as Mona -- and Toby -- knock out her entire mental Jenga tower, piece by piece.
Week: Meredith has Aria prisoner, thanks to her flu, and the other Liars are caught between tracking down the usual Cluelapalooza and actually taking Aria seriously for once. Paige and Mona, presumably, continue their downward mental spirals. Emily and Hanna get madder and madder and madder, hopefully. And even more hopefully, a reason is found to keep Lucas at Rosewood High.