The League of Assassins has played a huge part in Arrow over the past few seasons. Ra's al Ghul himself was the big bad of Season 3, and Oliver is still technically married to Nyssa al Ghul. We recently learned that Talia al Ghul is on the way for Season 5, but details were scarce about how she would appear. Now, Arrow star Stephen Amell has shared just how Talia will come into play in Season 5, saying this:
Given that the Season 5 flashbacks are taking place in Russia during Oliver's Bratva stage, Stephen Amell's tease about Talia's connection to the flashback plot may come as a surprise to fans. The League of Assassins storyline stayed firmly in the present in earlier seasons, and the only real connection to the flashbacks came in Season 3 with the reveal that Maseo had joined the League.
Stephen Amell unfortunately didn't elaborate in his chat with TVLine on whether or not Talia would appear in the flashbacks herself, but it would make a certain degree of sense. When Sara first brought up the League of Assassins way back in Season 2, Oliver had clearly already heard of them and seemed to know that they weren't just a myth. He had to learn about the League at some point, and it looks like that could be in the Season 5 blasts from the past.
There are a number of different ways that Arrow could mention Talia before Lexa Doig makes her debut in the role. The most straightforward is simply that Nyssa shows up in Star City again to drop some exposition about her big sister. She was on decent terms with Oliver and Co. when they last parted ways, and she's been a useful source of information to Team Arrow in the past. No matter if Talia debuts in the flashbacks or in the present, Nyssa could be a good way to tease her introduction.
Another way for Arrow to mention Talia would be for the Bratva brothers to start talking about her in the flashbacks. Anatoly has been another useful source of exposition, and it wouldn't be a huge stretch to imagine that the Bratva with all its shady connections would be aware of Talia al Ghul. Assuming Oliver doesn't get punched so hard by Dolph Lundgren that he's whacked all the way to Nanda Parbat, chatter about Talia could be a way to inform viewers before actually introducing her.
The third way is probably the least likely. If Oliver does have some flashback knowledge of Talia, he could share it with the audience via a conversation in the present with his pals about his time in Russia. Oliver is notoriously tight-lipped about his five years of hell, with even Felicity and Diggle mostly unaware of his activities during that time. We probably shouldn't expect Oliver to come clean about any past interactions with her unless he has no other choice.
Talia will make her first appearance in the flesh in Episode 10 of Season 5, so we still have a while to wait before we see her in action. Hopefully we'll start learning about her sooner rather than later. In the meantime, we can look forward to the big crossover extravaganza that will bring the heroes of Arrow together with the heroes of Supergirl, The Flash, and Legends of Tomorrow to battle some big bad aliens.