A lot of the promos for the upcoming sixth season of Arrow feature Katie Cassidy talking about her role as Earth-2 Laurel Lance.
Cassidy was part of the series from the pilot where she played Laurel, the ex-girlfriend of Oliver Queen (Stephen Amell). Oliver and Laurel's sister Sara (Jacqueline MacInnes Wood in Season 1, Caity Lotz in Season 2) went off together on the Queen's Gambit where they were both presumed lost at sea. And this is where the Earth 1 and Earth 2 Laurels differ.
The Earth-1 Laurel stays in Starling City, becomes a lawyer, dates Tommy Merlyn (Colin Donnell), deals with Oliver's return, deals with Sara's return. She eventually trains and takes up the mantle of the Black Canary, but dies in Season 4 at the hands of Damien Darhk (Neal McDonough).
Later that same year, over on The Flash Season 2, Zoom (Teddy Sears) is bring through villains from Earth-2 to help weaken the Barry Allen (Grant Gustin). One he pulls over is Black Siren.
This version of Laurel didn't stay in Starling after Oliver and Sara's disappearance. She went to Central City for a new start and got caught in the particle accelerator explosion like a lot of folks there. She gain the sonic scream ability and somehow turned to a life of crime. Earth-2 Oliver never came back from the island, even though Earth-2 Robert Queen (Jamey Sheridan) did in order to become a vigilante. After fighting the Flash, she made her way to Star City where she tried to pose as Earth-1 Laurel, eventually fighting the team. She hooked up with Prometheus (Josh Segarra) and helped him with his plan against Oliver.
Now Cassidy is back as a series regular, meaning we're going to get a lot of Black Siren this season. How will she play with Oliver and the team? Will she have more interaction with Quentin Lance (Paul Blackthorne)? The set up some unresolved issues there. It should be interesting to see who she fits in with the group of bad guys this season.
Arrow Season 6 kicks off on its new night and time, Thursday, October 12th at 9 p.m. following the thirteenth season premiere of Supernatural.