Michelle Dockery will star in the action-thriller 'Boy Kills World'.

The 40-year-old actress has boarded a cast that already includes Bill Skarsgard, Jessica Rothe, Andrew Koji, Yayan Ruhian and Isaiah Mustafa.

Moritz Mohr will make his feature directorial debut on the movie. Sam Raimi and Zainab Azizi will produce for Raimi Productions with Simon Swart and Wayne Fitzjohn also involved as producers via Nthibah Pictures.

The script has been written by Arend Remmers and Tyler Burton Smith.

Michelle is to play the sister of the film's Van der Koy family. Her character Melanie is a satirical powerhouse who attempts to project a cohesive family image to hide their decaying dynasty.

Fitzjohn said in a statement: "We welcome Michelle to the Van der Koy clan and the film. It is a perfect role for Michelle.

"It's an exciting time for the production with filming having begun just two weeks ago. We cannot wait to show the world the result."

Michelle has starred in a variety of roles – from the period drama 'Downton Abbey' to the crime caper 'The Gentlemen' – and explained that she doesn't have a particular career plan.

She said: "I don't tend to be strategic, in a way that's like, 'Okay, I need to do this now because I just did X, Y and Z before.' It really comes down to the writing and the character.

"Often, it's whether I feel something, in my gut, for the character."

Michelle will reprise her role as Lady Mary Crawley in the sequel 'Downton Abbey: A New Era' after admitting that the first movie "exceeded expectations".

She said: "We were thrilled and, like with any show you're a part of, you just never know what the appetite will be out there.

"Of course, people were wanting it to happen and willing it to happen, so we did it.

"But you never know how it's going to turn out.

"However, it exceeded our expectations."