'Sherlock' season 4 episode 2 spoilers: Sherlock meets Culverton Smith; Sherlock–John conflict gets worse

Sherlock Holmes (Benedict Cumberbatch) crosses paths with a new enemy on the upcoming episode of "Sherlock" season 4.

Titled "The Lying Detective," next week's episode of the top-rating BBC One drama will see the arrival of a new big bad. According to the official synopsis, Sherlock deals with perhaps the most chilling enemy of his long career as a detective: the seemingly invincible Culverton Smith (Toby Jones). Knowing he can't be trusted, Sherlock finds a way to discover Culverton's dark secrets.

After an almost three-year wait, "Sherlock" recently went back to the airwaves with a bang. Sunday's premiere kicked off with a 90-minute episode titled "The Six Thatchers," garnering about 8.1 million viewers. Despite the impressive overnight ratings, the episode is down by 1.1 million from the third season's premiere episode titled "The Empty Hearse," which remains as the series' highest-rated episode to date.

Fans are still trying to process what went down in the premiere episode when it featured the death of a major character: Mary Watson (Amanda Abbington). Many viewers were sad to see John Watson's (Martin Freeman) feisty wife go, leading to speculations that she could still come back. However, showrunner Steven Moffat recently clarified that killing off the character was necessary to bring Sherlock and John's partnership back to where it used to be.

"Sherlock Holmes is about Sherlock and Dr. Watson, and it's always going to come back to that — always always always," Moffat told Entertainment Weekly. "They had fun making it a trio, but it doesn't work long-term. Mary was always going to go, and we were always going to get back to the two blokes," he went on to say.

The previous episode also saw John lashing out at Sherlock after Mary's death, blaming him for what happened. Moffat added that the fracture in their relationship won't be resolved easily. "We take that rift head-on in the remainder of the [season]," the EP continued. "We don't ignore it... If anything, the rift gets worse," he added.

The fourth season of "Sherlock" airs every Sunday night at 9 p.m. ET on BBC One.