This is a typical episode in many respects: the A-plot deals with a frightening but not-particularly-interesting villain and the rest of the run-time is devoted to edging all our main characters toward the next bout of character development that's required for the overarching plot.
So let's get the least interesting bit over with first. Turns out that after the quake, several prisoners were able to escape Iron Heights prison, including a serial killer called Barton Mathis. In a nasty bit of grotesquery that seems more suited for The Silence of the Lambs than Arrow, he kills his victims by pouring a chemical down their throat before dressing them up like dolls. It's pretty gross actually.
Now Detective (or Officer, I suppose) Lance reaches out to Felicity for help in commissioning the vigilante's help. In this respect, the serial killer angle works, as it would have to be something extremely dangerous and extremely personal for Quentin Lance to forego his principles and resort to vigilantism. As it happens, he hunted down Barton Mathis in the months after Sara's death, and so ended up projecting his grief onto the myriad of dead girls that were left in the killer's wake.
Okay, so that's a nice bit of melding plot and character, though the ensuing "investigation" leaves a lot to be desired. Tracking down Mathis relies on a rather clumsy line of inquiry that relies upon his attorney knowing where he might be hiding, and all the girls' deaths being linked by the type of moisturiser they use.
I'll let you debate for yourself what's more unlikely: an attorney correctly guessing where one of the hundreds of his clients is hiding out (and being conveniently slimy enough to justify Oliver putting an arrow in his shoulder) or Mathis's amazing psychic powers when it comes to knowing what type of body-care products women are buying. It doesn't help that I'm currently watching The Fall, which goes to great lengths to demonstrate the time and effort it really takes for a predator to stake out a woman's habits.
Oh, and Laurel gets kidnapped. Again. Seriously, do these writers actively hate this character? Give the woman a break!
Which is as big a Deus Ex Machina as they come – but hey, if you're going to resort to one, then at least make it as cool as this.
It plugs in nicely to the other subplot that's been steadily threading its way throughout these episodes: Oliver using Roy to get information from the street. Following the orders of his would-be idol (by snagging some wine bottles from Verdant which Thea will no doubt follow up on in later episodes) Roy follows his contacts to a young woman called Cindy (or "Sin") and chases her to a clock-tower artistically draped in ... tissue paper?
Of further interest is the fact that she believes Roy has been "sent" by a mysterious "they", who by the end of the episode is revealed as the League of Assassins (whoohoo!) Even more pertinently, it appears that she's not averse to killing her opponents: first Mathis, and then the man who was sent after her. Hopefully this won't lead to a self-righteous spiel from Oliver – who after all, has only just decided to stop killing people himself – but a deeper look at the nature of vigilantism and assassins.
It seems notable at least that it's this episode that has Quentin coin the name "Arrow" for the first time.
I'm not sure how I feel about the portrayal of Mathis's first victim. The shots of the neck, hand and feet were certainly disturbing, but the lack of focus on the face made it oddly dehumanizing – which is surely not what they were going for.
Black Canary's trademark sonic scream has been "updated" to a device that blasts the eardrums of all those around her (except, oddly, Oliver himself). It would have been difficult to justify any organic ability to do this, so I'm cool with gadgets for now.
One day I'll find a way to say something substantial about the island flashbacks that requires me to put them somewhere other than the "miscellaneous observations" pile, but today is not that day. While Shado investigates a corpse, Oliver and Slade go a-wandering, and then make the idiotic decision to run through an area where missiles are being fired.
To say that the new vigilante (I suppose I can't call her Black Canary yet) is specifically targeting misogynistic criminals feels a bit too specific. I mean – how does she find them? And does she just ignore any other type of criminal she comes across if they're not menacing a woman? I've got nothing against this angle, but the logistics of it come as a bit of a stretch.
That said, I'm glad they let her be the one to kill Mathis. Remember, if you establish your new female character as someone who punishes the perpetrators of male-on-female crime, then it's imperative that you actually allow her to succeed at this.
Poor Thea is a bit side-lined this time around, but there's an interesting development regarding her mother. Paul from Orphan Black wants to initiate the death penalty, but Moira already seems to have mentally/emotionally checked out. She's in a good place with her children, and so she accepts her fate – though it appears she's still got something to hide from them.