Gotham's Selina Kyle has taken an important step toward becoming Catwoman.

On last week's episode, Selina (Camren Bicondova) pushed Wayne Enterprises spy — and would-be Alfred (Sean Pertwee) assassin — Reggie (guest star David O'hara) out of a window in order to keep him from tipping off his employer Sid Bunderslaw (guest star Michael Potts) that Bruce (David Mazouz) is onto him. Unfortunately, Selina's good intentions have serious consequences.

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"Part of her is glad she did it," Bicondova says in the exclusive behind-the-scenes video below. "[But] that's her first kill. I think for anyone it would be traumatizing." Indeed, Bruce is also reeling from Selina's choice. "The fact that Selina killed Reggie does affect Bruce and Selina's relationship in a very significant way," Mazouz says.

However, as seen in the clips from Monday's episode (8/7c, Fox) also in the video, the duo plans to attend a charity ball in order to learn more about Bunderslaw and what he's up to. But they might be biting off more than they can chew. "Alfred quite rightly warns [Bruce] that the evil heartbeat of Gotham city itself goes... to the top of Wayne enterprises," Pertwee says.

So, what secrets will Bruce and Selina uncover? Watch the video below and check out Gotham on Monday at 8/7c on Fox.