Mark Gatiss, co-creator and co-producer of Sherlock: I first came across [the Mind Palace concept] in Hannibal, the Thomas Harris book, and the idea of it is so thrilling. But in a way it’s an extrapolation from Doyle from Sherlock’s quote about a man’s mind being like a lumber room. It doesn’t have elastic walls. There comes a point where for everything you put in, you have to delete something. And that became in the first series comparing it to a hard drive, and really, that’s what it is.