Nyssa al Ghul (Katrina Law) will make her triumphant return to Arrow later this season, just in time for an epic confrontation with her half-sister Talia (Lexa Doig) in the Season 5 finale.
This information comes via an Entertainment Weekly exclusive that confirms their ongoing conflict will be part of a multi-episode arc. Nyssa was an antagonistic presence throughout Seasons 2 and 3, particularly during Oliver’s conflicts with the League of Assassins. Eventually, though, she became an uneasy ally to Team Arrow and mentor to Laurel after the two bonded over their mutual loss of Sara. Nyssa was, after all, in love with Sara from their time training together with the League after the younger Lance sister was discovered by the League. She had ongoing issues with Malcolm Merlyn, and convinced Team Arrow to help in the disassembly of the league. Nyssa’s last appearance on the show was at Laurel’s funeral in Season 4.
Don't forget that Nyssa is also still technically married to Oliver.
Talia, on the other hand, entered the show during Season 5 flashbacks training Oliver in Russia along with her own splintered clan of assassins. Despite ongoing issues with her father, she was spurred to help train Prometheus after she learned that Oliver killed Ra’s al Ghul, going on to be involved in the big identity reveal.
So far on Arrow, Talia and Nyssa have had very little to do with one another outside of their shared parentage. Each trained a lifetime and then some with the League of Assassins, so when their undefined conflict does come to a head, it’s bound to be an epic showdown.
Arrow returns to The CW after on April 23, 2017.
