Showtime’s adaptation of Edward St. Aubyn’s Patrick Melrose novels already has Benedict Cumberbatch in the lead and Jennifer Jason Leigh and Hugo Weaving playing Cumberbatch’s parents, and now another fairly famous person had joined the cast. According to Deadline, Allison Williams from Girls and Get Out has joined the cast as Marianne, a woman that Cumberbatch’s eponymous Patrick Melrose meets “during his playboy years in New York.”