"Sherlock " season 4 reveals Sherlock facing his toughest challenge ever, which is to baby sit John and Mary Watson's baby. Creators Steven Moffat and Mark Gatiss hinted at Sherlock's newest role in a teaser photo where the modern-day detective is looking curiously at Watson's baby.

Sherlock has been known to be a genius with an impeccable memory and unique logical thinking processes, which he calls his "mind palace." Here Sherlock taps his ability of recall and deductive analyses by casting all other thoughts aside to focus on the facts presented.

This is how Sherlock deduces and solves many of his cases, which to normal people is baffling enough to solve in a day, but Sherlock can do it in a matter of minutes. However, for "Sherlock" season 4, the functioning sociopath's abilities will be put to the test as he takes on the role of a babysitter to Watson's newest baby.

As to why and how Sherlock survives the day is undisclosed, but fans will be eagerly anticipating in this hilarious plot twist in an otherwise darker and more intense Sherlock in season 4. Teaser trailer released a few weeks ago hinted at a darker Sherlock seemingly wrestling with is inner demons.

Showrunners Moffat has already disclosed that there will be consequences that Sherlock will have to deal with in "Sherlock" season 4. The modern-day detective will also be facing the most evil villain to date, Culverton Jones played by Toby Jones is an expert in tropical diseases and will even infect Sherlock in an episode aptly title "The Adventures of the Dying detective" according to Cinema Blend.

Moreover, "Sherlock" season 4 will be bringing Tom Hiddleston to 221B Baker Street as the missing third brother, Sherrinford Holmes. This rumor surfaced after creator Gatiss posted a picture with Hiddleston with the caption "blud" for brother.

Just recently, BBC released a teaser trailer called "The Rising Tide," showing Sherlock and John sitting pensively in their old room with flood waters rising to their ankles as reported in Deadline. Fans have speculated that the video reveals so many clues pointing to Moriarty and Sherrinford. Soon, all these rumors will be put to rest for "Sherlock" season 4 airs on January 1, 2017.