'The Bachelor' sneak peek: Colton tries to figure out who's the 'cancer' in the house

Courtney and Demi face off in a game of espionage on this week's episode of "The Bachelor."

Both women vying for Colton Underwood's affections try to get in the bachelor's head to convince him the other is a "cancer" in the house.

In a sneak peek of Monday night's show, Colton speaks to Courtney, telling her that Demi has been badmouthing her.

"The words being attack and you being the cancer of the house were brought to my attention," he says.

Courtney says that even her worst enemy in the world would never say that about her.

"If anyone isn't here for the right reason, it's Demi," she tells Colton. "You could be anybody. The fact that you're the bachelor and the fact this is a TV show is the reason she's here."

The words seem to get to Colton, who says this is his "worst nightmare" come to life.

"Is the Demi that I see the real Demi?" he questions.

Check out the clip above and an all-new episode of "The Bachelor" tonight at 8 p.m. on ABC!

Join the Official Bachelor Fantasy League to compete with family, friends and the rest of #BachelorNation for a chance to win a Grand Prize trip! Set your own weekly lineup of Bachelorettes based on weekly categories ranging from who will get a rose to who kisses Colton. Click here to learn more!