So far this season, Arrow has wisely concerned itself with reestablishing some ground rules as far as what the series should and should not task its hero and his teammates with in their pursuit of justice. Aside from taking a week off to shoot some aliens and remember all the characters that have come and gone over the past four seasons (and some change) that refocusing has resulted in an improved season overall, one that has again introduced the idea that Oliver Queen's mission is to save Star City. And, as far as daunting tasks go, that one is a biggie. But that task is about to get even bigger as Ollie and the new Team Arrow find themselves the targets of the mysterious Prometheus, who just so happens to have everyone's secret identities and an ace up his sleeve in the form of Evelyn Sharp – otherwise known as Team Arrow's archer-in-training Artemis.

The reveal that Evelyn was Prometheus' mole inside the Arrow organization during 'Vigilante' made for a solid twist that not only threatened the already shaky foundation upon which the new team was built, but it also elevated Artemis from a tertiary character to someone who could potentially have a great impact on the story moving forward. 'What We Leave Behind' offers her the chance to do that, as her affiliation with Prometheus is revealed along with her motivation for betraying her team and siding with the other masked archer (man, between this show and The Flash, villains really need to do a better job of creating an identity that isn't the dark version of the hero). As it turns out, Evelyn and Prometheus aren't just looking for vengeance against Oliver Queen; they're sitting in judgment of him and his tenure as Star City's protector – an effort they have deemed to be a failure.

The notion that Prometheus and Evelyn are turning Oliver's "You have failed this city" line around on him adds a fun bit of symmetry to the idea that a pair of masked archers is holding the original masked archer accountable for his actions. It's the comic book version of an oversight committee run amok. But considering Arrow still hasn't revealed Prometheus' true motivation – much less his (or her) identity – there is still plenty about the villain to uncover in order to further build intrigue and tension between Green Arrow and this villain with ties from his past.

The episode makes a considerable effort to trace the motivations of Prometheus back to Oliver's murder of a wealthy industrialist name Justin Claybourne. This was back during season 1 of Arrow, which gives the show a chance to take the original Arrow (or the Hood) costume out of storage and, through one of the more technically interesting sequences in the hour, match Oliver's actions the night he killed Claybourne to the moment he confronts Prometheus. It's a callback to the sort of thing the show did back in season 2 – especially during the climactic confrontation between him and Slade Wilson in the finale. In that sense, it's nice to see Arrow up to its old tricks, since this is the sort of thing the show is clearly good at and could stand to use more often. But the sequence also works as a proof of concept for using a different kind of flashback once the five-year flashback plan has run out. It's not necessary for the show to keep the format, and it certainly doesn't seem like most of those who watch would mind seeing the flashbacks go. But if adding a flashback narrative was determined to be absolutely imperative by the producers, cutting back to the early days of Oliver as the Hood clearly makes for some interesting compositions.

Here, though, the sequence is necessary to build suspense for the confrontation since the show is still keeping Prometheus's identity a secret – even though the hour leans heavily on his being the illegitimate son of Claybourne. Either way, it seems the man stalking Oliver, murdering dozens of people in Star City, tricking him into killing Felicity's new boyfriend Billy, and nearly killing Curtis in front of his husband is a figure from the past, just not someone Ollie or the audience knew about until now. For it to be a brand new character and not one long thought to be dead is the less comic book-y road to travel down, which is refreshing as it demonstrates the show's willingness to invest more in the thematic idea of Oliver taking stock of the road he took to becoming the Green Arrow – a road paved with bodies of people who failed Starling City – rather than a shocking revelation that, say, Tommy Merlyn is somehow still alive. There's always a chance the villain will work out to be someone else, and like not counting a character dead until you see the body (and sometimes not even then, as the show demonstrates in a cliffhanger that should have included a record scratch audio cue), there's no telling who's behind Prometheus's mask until it's pulled of.

To that end, the surprising reveal that Laurel is hanging out in the Arrow Bunker feels so far removed from anything that happened during the hour that the cut to black after she says hello is tantamount to a slap in the face. Her arrival is seemingly without context, there doesn’t seem to be any way of telling whether her return is real or imagined, or if it is somehow related to Prometheus and the questions of his identity. While it feels like a cheat on behalf of the show, a way to get the audience riled up ahead of the winter hiatus, one has to wonder whether or not Laurel's presence is tied to some lingering aftereffects from the Dominators or if she is a portent of things to come with regard to who is really behind the Prometheus mask.

For the midseason finale to end on as unexpected a question as Laurel's return is frustrating, especially given the series' past disappointments with bringing characters back from the dead. Furthermore, it undercuts the urgency of Prometheus and the emotional gravity of Oliver killing Billy. It's likely that the Arrow writers have a trick up their sleeves in answering the many questions that stem from this cliffhanger, but this sort of trick threatens to weaken the foundation of what has been a solid season so far. Hopefully whatever the answer is, it won't pull season 5 off the path it's been on.

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Arrow season 5 will continue in January 2017 on The CW.