One of the unexpected pleasures of TV in the past couple of years — along with “The Walking Dead” and a handful of other shows — has been “Sherlock,” Steven Moffat’s modern-day updating of Arthur Conan Doyle’s Victorian-age detective Sherlock Holmes.

There have been so many — hundreds — of stage, film and TV adaptations of the Conan Doyle books and short stories in the past century years that it’s hard to imagine crowning one as the best, particularly one that takes such liberties with the content of the canon. But “Sherlock,” a BBC production airing on PBS’ “Masterpiece” series (with two more installments to come May 13 and 20) is certainly near the top of the list.

In the series, set in the present day, Holmes (Benedict Cumberbatch) and Watson (Martin Freeman) forge the offbeat relationship familiar to readers of the original stories. Holmes is a brilliant consulting detective, Watson a physician and soldier. Each man is troubled in some respects. Watson is recovering from physical and spiritual wounds suffered in Afghanistan while Holmes is, for all his British intellect and wit, a stranger in a strange land.

The updated series uses original Conan Doyles stories (and titles; tonight’s episode is a take-off on “A Scandal in Bohemia”) as jumping off points, mixing in high-tech touches along with Holmes’ old-school detective work. In other words, for every scene in which Holmes deduces someone’s life story by observing stay hairs on their pants or scuffs on their shoes, there’s another scene in which Holmes or one of the players is texting on their smartphone. Just as Conan Doyle’s original writing had Watson publishing stories about his exploits with Homes — much to Holmes’ bemusement — in the new series, Watson writes a popular blog about the detective.

Tonight’s episode, like the 1891 original, introduced Irene Adler, a woman who is Holmes’ equal in sheer, cool intellect. In “Sherlock,” Adler is a high-society dominatrix who, as the  episode opens, is being sought for the compromising photos of a member of the royal family on her cell phone.

Adler is, as fans know, “The Woman,” the female who greatly intrigued Holmes, who was very likely his perfect match … if not for her habit of lawbreaking.

In “Belgravia,” we get some choice “Sherlock” scenes, as Holmes stays one step ahead of the police and the bad guys even as he struggles to keep up with Adler.

All the key ingredients to the “Sherlock” series are here: Holmes and Watson’s fond verbal jousting; landlady Mrs. Hudson; even Holmes’ nemesis James Moriarty. The opening of the episode resolves the standoff between Holmes and Moriarty from the end of the first season.

“Sherlock” revels in its modern-day ingenuity — the use of technology and London’s cool blue exteriors give the series a properly detached feel — as much as it encourages us to focus on Holmes’ never-out-of-style intensity.

Cumberbatch and Freeman are among the best portrayers of Holmes and Watson ever. Cumberbatch gets a showy role but Freeman — soon to star in “The Hobbit” with Cumberbatch providing the voice of the dragon Smaug — is an understated delight.

“John Hamish Watson. Just in case you’re looking for baby names,” Watson mutters at some point when Holmes and Adler are striking sparks.

And what an Alder Lara Pulver is. I love Rachel McAdams, who plays Adler in the current Robert Downey Jr. Holmes movies. But Pulver makes McAdams look like the high schooler she played in “Mean Girls.” Pulver, who matches Cumberbatch in cheekbones and ivory skin, is gorgeous and dangerous. She’s utterly believable as “the woman” in Holmes’ life.

Next week, “Sherlock” takes on “The Hound of the Baskervilles.” I’ll be watching.