[SPOILERS for those not caught up on The Flash Season 2 ahead.]
The second season of The Flash has continued the previous season's trend of pushing the story forward at a brisk pace. Most weeks see the introduction of a new villain, who plays a minor role in the overarching story of the season's main antagonist. Season two sees Barry Allen (Grant Gustin) facing off against his greatest foe yet: Zoom (Tony Todd), a maniacal speedster who wants to steal the Speed Force from Barry's body.
Fans will remember that Zoom isn't the first villain in the series to match Barry's speed. Early in season one, it was revealed that his mentor, Harrison Wells (Tom Cavanagh) had a connection to the villainous yellow speedster that killed Barry's mother. However, it wasn't until later that the writers revealed the truth behind that connection - the real Harrison Wells was dead and a time traveling speedster named Eobard Thawne (Matt Letscher) had assumed his identity. Proving to be more than a match for Barry, it was ultimately the sacrifice of Eddie Thawne (Rick Cosnett), Eobard's distant ancestor, that defeated the villain and removed him from the timeline entirely.
In classic comic book fashion, Harrison Wells is back in the current season of The Flash (albeit a version from another dimension). The series' introduction of the multiverse allowed him to return to the series, but it turns out he's not the only dead character to resurface. Speaking with EW, Flash executive producer Todd Helbing confirmed that Letscher's Eobard Thawne will also be returning to the show. Elaborating briefly, Helbing said the following:
"His impossible return to Central City puts a member of the S.T.A.R. Labs team in unexpected danger, forcing Barry to make a life-changing decision."
There are no further details about the character's return, but it will likely involve the alternate dimension Earth-2 - the source of many of this season's new villains. Eobard will return in the eleventh episode of the second season, the second episode to air after The Flash returns in January. Appropriately, the episode is titled "The Reverse-Flash Returns."
The relationship between Barry and the Reverse-Flash has proven to be one of the most important in the series, not only in an antagonistic sense but in developing the majority of the characters. Thawne's actions and betrayal have had a lasting effect, specifically in regards to Earth-2 Harrison Wells. With Barry finally moving on from that betrayal and learning to trust the new Wells, there's no better time to reintroduce Thawne and change the show's status quo.
The creators of The Flash are currently filling out the ranks of the villains for the second half of season two. The show recently cast Marco Grazzini (Heroes Reborn) as the villain Tar Pit, as well as Adam Stafford (Neighbours) as Geomancer. The latter half of the season is also expected to explore newcomer Wally West (Keiynan Lonsdale), introduced in the last moments of The Flash's winter finale.
The Flash will return on Tuesday, January 19, 2016, while Arrow will return on Wednesday, January 20, 2016 and Legends of Tomorrow will see its series premiere on Thursday, January 21, 2016.