Sherlock season 4 kicks off with an episode titled, “The Six Thatchers.” Here is everything you need to know about the original Conan Doyle case, “The Six Napoleons.”

The season 4 premiere of Sherlock kicks off with a “smile, but turns as dark as oil.” Choosing to kick off the season with an adaptation of “The Six Napoleons” runs the two detectives through a classic Conan Doyle tale.

It’s an opportunity to get viewers back in the groove of Sherlock and Watson out and about and explore what has or has not changed between the two now that baby Rosamund is on the scene.

Previewing season 4, Benedict Cumberbatch notes that Sherlock is “seemingly indifferent which is comic at times but it’s all underpinned with a deep love and he’s a guardian angel really.”

Before you kick off the new year with new Sherlock, here is an overview of the original case!

The Case

Breaking and entering cases are not exactly Sherlock’s cup of tea. But when the case involves a man bent on taking out his aggression on a long deceased political figure, the detective’s interest peaks.

Three busts of Napoleon rest in pieces on the floors of various homes and shops. The fourth destruction produces a victim. However the murder is not the clue Holmes needs to solve the case. It is the location where the fourth bust meets its end — someone’s front yard under a street lamp.

The Solution

Dr. Watson lends a helping hand on the mental state of this man’s fixation with Napoleon. However, it is all for not when Holmes deduces the true motivation for the crime spree. A man recently let of prison once worked in a plaster factory where right before his capture for a jewel heist, created a cast of Napoleon.

Six figures were made from that cast and in one of the productions the criminal, Beppo, hid the Borgia pearl. After his release, Beppo goes in search of busts and smashes them until Holmes and Lestrade catch him in the act.

Holmes finally pays a man in possession of the final bust a modest sum to take the item off his hands. After smashing it open, he reveals the Borgia pearl to Lestrade and Watson.

The Adaptation

Expect to see the plaster casts feature a more recent British figure, Margaret Thatcher. While the mystery updates itself for the modern Sherlock audience, the base of the story remains rather close to canon.

Of course this is only the background noise for what develops this season. The first case of the season will bring laughter and a few learning curves for the detective. But it will also set the stage for the darker elements to take over as we head into episodes 2 and 3.

“The Abominable Bride” and “His Last Vow” takes viewers into the mind of Sherlock Holmes. This landscape returns as the detective comes faces a new opponent, Culverton Smith.

Benedict Cumberbatch comments on the great detective’s mind saying, “The way he engages with [the world] often blinds him to the most obvious… His stupidity is also the world’s brilliance which is why there are things, people, and events, which overtake him.” That is partially why the trips inside his head, whether under the influence of drugs, or not, is an intriguing angle for storytelling.

Cumberbatch also reminds us, “He’s not unhuman, he is human and he is fallible.”

Are you looking forward to ‘Sherlock’ season 4?

Sherlock season 4, episode 1 “The Six Thatchers” premieres tonight at 9:00 p.m. on BBC One in the UK and 9:00 p.m. on PBS in the U.S.