Bill Condon’s forthcoming Sherlock film A Slight Trick of the Mind has nabbed its second cast member in Laura Linney.

Linney will play Sherlock Holmes’ housekeeper Mrs. Munro, according to Entertainment Weekly. Munro has a son who Sherlock takes a “parental interest” in.

Sherlock himself will be played by Ian McKellen who’s best known for his role as Gandalf in The Lord of the Rings and The Hobbit.

In an interview released today on EW, Linney spoke about how big of a fan she is of Sherlock. “I was obsessed with Sherlock Holmes as a young kid,” Linney said. “You know how some people are into Dungeons & Dragons? I was into Sherlock Holmes. I loved the atmosphere of the stories. I loved the intrigue, his personality. Bill had no idea.”

Linney and Condon worked together before on his 2004 film Kinsey.

A Slight Trick of the Mind begins filming this summer in the United Kingdom. Although it will be set in Holmes’ older years as a 91-year-old battling being an elder (as he keeps bees in Essex), the film will also look at his life at the age of 63 as he works on his final case.

Said Condon to EW about Linney and McKellen, “I’m looking forward to the combined talent, skills, and smarts. Both of them are incredibly detail-oriented and do an amazing amount of work before they get to set, and then they dive off the board and become their characters.”

The project was first revealed in September. It is based on the book of the same name by Mitch Cullin – grab it here via Amazon.