The shot shows Sherlock pointing out something to a dog, who could be helping him with a case. The breed appears to be a Bloodhound, which is often used as a scent hound, the kind of canine law enforcement relies on to track or trail humans thanks to their keen sense of smell.
Sherlockians also already know the legendary detective used a dog named Toby to help him in Arthur Conan Doyle's Sherlock adventure "The Sign of Four." Dr. Watson describes the dog as an "ugly long haired, lop-eared creature, half spaniel and half lurcher, brown and white in color, with a very clumsy waddling gait."
Speaking of Watson, even though Sherlock's usual crime-fighting companion played by Martin Freeman isn't in this first photo, he is returning to the series. So is Mycroft Holmes (Mark Gatiss), Molly Hooper (Louise Brealey), Mary Watson (Amanda Abbington), Mrs. Hudson (Una Stubbs) and DI Lestrade (Rupert Graves).
In May, BBC announced actor Toby Jones would play a mysterious villain in the second episode of the next season of "Sherlock." An air date for "Sherlock" season 4 has yet to be announced.