Eddie Marsan (“Ray Donovan”) has joined the cast of an untitled murder mystery opposite Patrick Wilson, Jessica Biel and Haley Bennett.

The project was unveiled at Cannes with Sierra/Affinity handling international sales and CAA overseeing the sale of the project domestically. The film has started production in Cincinnati.

Andy Goddard, who helmed the third season finale of “Downton Abbey,” is directing. He’s been attached to the project — formerly known as “The Blunderer” — since early last year. It’s based on Patricia Highsmith’s novel “The Blunderer.”

Producers are Killer Films’ Christine Vachon and David Hinojosa, along with Ted Hope and Sierra Pictures, which is also financing with 120dB Films and Electric Shadow.

Susan Boyd adapted the 1954 novel, which Highsmith wrote in between “Strangers on a Train” and “The Talented Mr. Ripley.”

Highsmith’s novel is centered on a successful and handsome man (Wilson) who seems to have it all until the day the body of his wife — played by Biel — is found at the bottom of a cliff. Under the intense scrutiny of the investigation, he commits one mistake after another until he finds his perfect life derailed.

Executive producers are Sierra/Affinity’s Nick Meyer, Marc Schaberg and Kelly McCormick, 120dB’s Stephen Hays and Peter Graham, Electric Shadow’s Alexa Seligman, Jay Taylor and John Jencks, and Miscellaneous Entertainment Finance’s Joe Simpson.

Sierra/Affinity has sold the project in over 25 territories. Sony Pictures Worldwide has bought the film for Australia, Benelux, Latin America, Scandinavia, South Africa, Spain and the U.K. Wild Bunch has bought German rights.

Marsan’s credits include the two “Sherlock Holmes” movies, “War Horse” and “Filth.” He repped by UTA and Markham, Froggatt and Irwin in the U.K.