TVLine reports that Lithgow will appear across from titular star Matthew Rhys, and will be playing Elias Birchard “E.B.” Jonathan. The site describes the character as "a personal attorney (and semi-regular employer of Mason) who is at a low point in his career. A mentor and father figure to Mason, E.B. is handed the kind of case he hasn’t seen in years: a high-profile parallel investigation to the Los Angeles Police Department involving a child kidnapping."
Both Jonathan and Mason are going through hard times, as the series picks up with Mason -- who's depicted as a defense attorney in the Erle Stanley Gardner novels on which the adaptation is based -- during a period where he's working as a low-rent private investigator, trying to get his life back on track after a stint in the war and a failed marriage. Sounds like some juicy material for Lithgow and Rhys to work with -- and definitely something we can't wait to see the Emmy winners (for "The Crown" and "The Americans," respectively) tackle.