According to showrunner Greg Berlanti, tonight's episode of The Flash was "crafted as part one of a two parter. And that's all I'll say about that."
Next week's episode revolves around a "surprising ally" coming to Barry's aid as he hatches a dangerous plan to face off against Zoom.
...And there are a few possibilities there. The most obvious one is that the surprising ally is Doctor Light. She appears in tonight's episode, "The Darkness and the Light," but even though she's the episode's primary threat, it's said that she isn't a bad guy on Earth-2.
Another possibility? Jesse Quick could be the ally.
Executive producer Andrew Kreisberg said on Twitter that Violett Beane will debut as Jesse Quick tonight, and Beane had responded to Berlanti's earlier "part one of a two-parter" tweet with a "Hmm..." and a smiley face.
The Flash airs Tuesday nights at 8 p.m. ET/PT on The CW.