How can you follow up with a villain so delightfully fun and yet also so maniacal as Andrew Scott's Moriarty? Find someone scarier, apparently.

Sherlock co-creator Steven Moffat opens up about season three's villain, Charles Augustus Magnussen, played by Lars Mikkelsen: "We needed an utterly terrifying villain and Lars just scares the crap out of you the moment he shows up!"

Mikkelsen's character is based on the "master blackmailer" Charles Augustus Milverton from Conan Doyle's books, but Moffat decided to slightly alter the character's nationality once he decided to cast the Danish actor. "We had a notion that maybe he might be American and at that point we kept the original name... It was actually [producer] Sue [Vertue] who originally suggested that we have a look at Lars. I then went onto a website and looked up all the Danish names that sounded a bit like 'Milverton' and came up with Magnussen!" he explained at a BAFTA screening of the season finale.

Although British fans will get to tune into the third season's finale - titled "His Last Vow" - this Sunday, Americans will have to wait until February 2 when it airs on PBS.