‘Sherlock Season 4, Episode 3 Spoilers: ‘The Final Problem – Sherlock, Watson Face “Greatest Challenge”; Mark Gatiss Promises Lots of Action

‘Sherlock’ season 4’s episode 3, titled “The Final Problem,” is set to feature Sherlock and Watson as they face their “greatest” challenge. Meanwhile, Mark Gatiss promised that the season finale will bring in lots of action and “more fighting.”

The synopsis for “The Final Problem” posted on TV Muse reads, “In the final episode of this series, written by Mark Gatiss and Steven Moffat, long-buried secrets finally catch up with the Baker Street duo. Someone has been playing a very long game indeed and, alone and defenseless, Sherlock (Benedict Cumberbatch) and Dr. Watson (Martin Freeman) face their greatest ever challenge. Is the game finally over?”

The promo for the incoming episode teased a potential resolution for the Sherrinford/Euros storyline. In the preceding episode, titled “The Lying Detective,” it was revealed that Eurus (Sian Brooke) is the third secret Holmes sibling.

The existence of the third sibling was teased in season 3’s final episode, “The Last Vow,” when Mycroft Holmes (Mark Gatiss) said that he didn’t have brotherly compassion, and told someone that they "knew what happened to the other one".

Eurus is revealed to be quite cunning and a mistress of disguises. She pretended to be a flirty bus passenger, Sherlock’s therapist as well as Culverton Smith’s (Toby Jones) daughter Faith before revealing her true identity. According to Mic, Eurus pointed a gun at John's head before pulling the trigger by the end of “The Lying Detective.”

It seems possible that “the greatest ever challenge” alluded to in the synopsis could refer to Sherlock’s long-lost sister. Eurus may pose a huge threat to the Sherlock and John in the incoming episode. During a previous interview with TV Line, Gatiss admitted, “There is quite a lot of action… Episode 3 is probably more action-packed than we’ve done for a long time, if ever. Definitely more fighting.”

‘Sherlock’ season 4’s episode 3, titled “The Final Problem,” is scheduled to air on BBC One in the UK and PBS in the US on January 15, 2017. It was directed by Ben Caron and written by co-creators Steven Moffat and Mark Gatiss.

The crime-drama television series is based on the iconic fictional detective created by Sir Arthur Conan Doyle and stars Benedict Cumberbatch as the titular sleuth, with Martin Freeman co-starring as his friend and partner Dr. John Watson.