WATCH: Jessica Chastain and Colin Farrell Go Head-to-Head in 'Ava' Trailer

Jessica Chastain is set to portray a killer for hire in the forthcoming thriller Ava, starring in the title role, reports Empire online. John Malkovich will take on the role of her handler, named Duke. He's cheering for her, being his protégé and all.

But, there is someone who is... not.

Enter Colin Farrell as Simon. We don't get his exact job title from the new trailer, but he seems to be Duke's boss. Simon has a problem with Ava's kill style, screaming at Duke, "She's talking to the targets!!"

Yeah, that might be a problem, as she's giving the mark a chance to get away. As well, she's showing empathy and may turn disloyal to her employers at some point.

Duke tries to help her, warning her, "Keep your head down. Management is watching you."

Does she take his advice? Not really — you can see what she does instead in the first look trailer below:

Matthew Newton (Who We Are Now) has written the script, with The Girl on the Train's Tate Taylor directing.

You can look for Ava in theaters on September 25.

Does Ava remind you of anyone??