Barry Allen has done in his first TV season as the Flash, but the scarlet speedster accomplished something totally groundbreaking in last night's episode: he traveled through time. That development, in addition to some other big mind-blowing twists that you can read about in our recap, made last night's episode one to go back and Hulu if you missed it as it aired.

If you did catch the pivotal episode, then you know that big things are coming next week as "The Flash" races towards its season one finale. In addition to hopefully tying up a few loose ends, the "Rogue Time" episode will include the return of Captain Cold (Wentworth Miller) and Heat Wave (Dominic Purcell) to the show, and it will feature the debut of "Mad Men's" Peyton List as Cold's sister, Lisa.

"Rogue Time" airs on March 24 on the CW. You can check out the trailer and synopsis below.

CAPTAIN COLD AND HEAT WAVE RETURN TO CENTRAL CITY; PEYTON LIST GUEST STARS AS LISA SNART - The Flash (Grant Gustin) learns that Captain Cold (guest star Wentworth Miller) and Heat Wave (guest star Dominic Purcell) have returned to Central City. This time Snart has brought along his baby sister Lisa (guest star Peyton List) to help wreak havoc on the city. John Behring directed the episode with story by Grainne Godfree and teleplay by Brooke Eikmeier & Kai Yu Wu (#116). Original airdate 3/24/2015.