The Flash has made the most of that gateway to Earth-2 that Barry (Grant Gustin) accidentally opened when he dabbled in time travel at the end of season 1. The series has used the alternate world to introduce a host of new villains to challenge Team Flash, including the biggest bad guy of all, the seemingly undefeatable Zoom.
Earth-2 also introduced the doppelgangers of characters we already know, many of whom have taken a different path than their Earth-1 counterparts. Barry never became The Flash, and he married Iris (Candice Patton). Meanwhile, Caitlin (Danielle Panabaker) and Ronnie (Robbie Amell) went to the dark side, transforming into Killer Frost and Deathstorm. Now fans will be treated to a doppelganger that's only interacted with Team Flash on crossover events.
While Arrow's Black Canary (Katie Cassidy) is well-known, especially to Cisco (Carlos Valdes), who created her signature sonic weapon the Canary Cry, Barry and his friends will soon encounter a whole new version of her. Arrow executive producer Marc Guggenheim has confirmed, via TVLine, that Cassidy will appear on The Flash as Earth-2's version of Laurel, Black Siren.
Donna Nance, who fought crime as the Black Siren, is a character from the Justice League animated series. She was based on the Golden Age Laurel Lance of DC comics, and existed in a virtual-reality city on a parallel Earth. This makes her the perfect inspiration for The Flash's Earth-2 character, though it's a strong possibility this Black Siren may exhibit a darker side, like many of the doppelgangers we've seen so far.
Though Team Flash worked together with Earth-2's Harrison Wells (Tom Cavanagh) to close the rifts between their worlds, it's been clear from recent episodes that Barry won't rest until Zoom has been defeated. Now that he's traveled back in time to find a way to increase his speed, the next step is getting back to that alternate Earth. The two speedsters face off in the next episode, airing April 19. Black Siren won't appear until episode 22 on May 17, so it's not clear yet what state Earth-2 will be in when we meet up with Laurel's alter ego.
There's also been some speculation that Cassidy's appearance on The Flash confirms that her Black Canary character will be the victim in that graveyard scene Arrow teased with its very first episode this season. While it's possible Laurel could meet her end on Arrow, guest-starring for one episode of The Flash isn't an obvious indicator, despite Cavanagh and Amell's post-character death appearances on Earth-2. Plenty of characters with doppelgangers are still alive and well on both worlds, so we'll have to wait a little longer to find out the fate of both Laurels.
Arrow continues Wednesday with ‘Eleven-Fifty-Nine’ at 8pm on The CW. The Flash returns with 'Versus Zoom' on Tuesday, April 19 at 9pm.