“Downton Abbey” alum Michelle Dockery and “IT” star Jaeden Martell have signed on for lead roles in the Apple limited series “Defending Jacob,” Variety has learned.

They join previously announced series lead Chris Evans. The series is based on the 2012 best-selling novel of the same name by William Landay. It tells the story of Andy Barber (Evans), a father whose 14 year old son Jacob (Martell) is accused of murder. Dockery will star as Laurie Barber, Andy’s wife and Jacob’s mother.

In addition to her Emmy-nominated role as Lady Mary Crawley on “Downton Abbey,” Dockery also received an Emmy nod for her role in the Netflix western limited series “Godless.” She most recently starred in the TNT series “Good Behavior. She will also reprise her role for the “Downton Abbey” film, which is set to be released later this year, and will star in Guy Ritchie’s upcoming film “Bush.” She is repped by WME, Anonymous Content, Hamilton Hodell, and Gang Tyre.

Martell (formerly Lieberher) starred as Bill Denbrough in the hit feature remake of “IT” and will reprise the role in the upcoming sequel. He previously starred in the Golden Globe-nominated film “St. Vincent” as well as the films “The Book of Henry” and “Midnight Special.” He will also star in the upcoming Rian Johnson film “Knives Out.” On the TV side, he appeared in nearly a dozen episodes of the Showtime series “Masters of Sex.” He is repped by CAA and Emily Cho Management.

The series was created, written, and executive produced by Mark Bomback, who will also serve as showrunner. It will be produced by Paramount Television and Anonymous Content, with Rosalie Swedlin and Adam Shulman executive producing for Anonymous Content. Academy Award-nominee Morten Tyldum will executive produce and direct the series. Evans will also executive produce.