SPOILERS for those not caught up on The Flash ahead.
Citizen Cold joins forces with Team Flash in the trailer for next week's episode of The Flash season 4, 'Fury Rogue'. Wentworth Miller has been playing the supervillain-turned hero Leonard Snart, aka. Captain Cold, in the Arrowverse since The Flash season 1, and was even promoted to being a main character in DC's Legends of Tomorrow season 1. Following Snart's heroic sacrifice in the Legends season 1 finale, viewers were then introduced to Leo Snart, Leonard's Earth-X counterpart aka. Citizen Cold (also Miller), during last year's "Crisis on Earth-X" crossover event.
Miller's unexpected journey across the Arrowvere now comes full circle, as he returns to The Flash for what could actually be his final performance as any iteration of Mr. Snart. Citizen Cold is arriving just in time too, as Team Flash took a heavy hit in this week's season 4 episode, 'Lose Yourself'. Barry Allen and his friends' efforts to take down season 4's big bad The Thinker, aka. Clifford DeVoe, by breaking into his lair not only failed, it resulted in the "deaths" of two members of Team Flash. Even worse, The Thinker may now have his sights on absorbing the powers of arguably the most dangerous "bus meta" created by Barry's return from the Speed Force, Neil Borman aka. Fallout (Ryan Alexander McDonald).
Related: The Thinker Claims Two More Victims
The trailer for the episode (see the video in the space above) confirms that Borman is the "dangerous meta" mentioned in the 'Fury Rogue' synopsis released last week. Borman, as Leo notes in the trailer, is essentially a "nuclear bomb" in human form and nearly destroyed Central City the last time viewers saw him in the episode 'The Trial of The Flash'. As such, Barry could use Leo's help in keeping Borman (literally) cool and preventing him from exploding before either his condition worsens or The Thinker gets ahold of him.
Miller, for his part, has indicated that he is open to reprising Captain/Citizen Cold in the Arrowverse again in the future, saying he loves the character and "It just has to be the right story." That further implies that 'Fury Rogue' won't kill off Citizen Cold and will leave the door open for his return to The Flash in the future. Nothing is certain though, and it's possible that this episode will instead grant the Earth-X version of Leonard Snart a heroic sendoff, similar to what Legends did for Captain Cold.
Of course, the more pressing matter is that of Fallout and what will happen if either he explodes (again) or The Thinker gets ahold of him. Even now that Mr. DeVoe has found a way to resume his original human form (welcome back to the cast, Neil Sandilands), it's not altogether clear what his ultimate end game even is, much less how he intends to execute it. Could it have something to do with Harry (Tom Cavanagh), who appears to be in danger of going off the deep end himself, due to his use of his own Thinking Cap?
The Flash continues Tuesday, April 24 with 'Fury Rogue' on The CW.
Source: The CW