It's rare to see the cool, calm and collected Red Reddington (James Spader) shaking in his boots on NBC's The Blacklist, but on Thursday's episode, he comes pretty close.

This week, we'll meet an enemy that poses a huge threat to Red, in more ways than one: Isabella Stone (guest star Melora Hardin).

As Red warns Liz (Megan Boone) in this exclusive clip, Isabella (not her real name) is "quite literally a character assassin. Her objective is to utterly obliterate her target by any means necessary — scandal, public humiliation, extortion, theft, murder."

And she's got her sights on Red, as evidenced by the fact that his associates keep mysteriously dropping like flies. But what's an even bigger threat to Red than his reputation potentially being ruined? It seems as though Isabella is willing to destroy anyone and anything in her path to get to Red — and that includes Liz.

The Blacklist: Will Tom's killer instinct tear him and Liz apart?

Check out the clip to see Red's warning to Liz, as well as a cryptic reference to the fact that, apparently, Tom's (Ryan Eggold) father has come back into the picture.

The Blacklist airs Thursdays at 10/9c on NBC.