SEASON PREMIERE: It’s been seven years since Sherlock arrived on PBS, bowling over critics and viewers instantly with its fresh take on the Sir Arthur Conan Doyle mysteries, and making a star of Benedict Cumberbatch as Sherlock Holmes. (Martin Freeman, as his Dr. Watson, already was a beloved British figure, thanks to his co-starring role on the original BBC incarnation of The Office.) And not counting the most recent, stand-alone Christmas special, Sherlock hasn’t given us a new installment in three years, so this is a very welcome return. But it’s a brief one, only three episodes long, so enjoy them while you can. (It seems that just as U.S. television finally is adapting to the British model of shorter TV seasons, the Brits are adapting too, to a mini-model.) This fourth season opens with The Six Thatchers, and is based on the Holmes story in which someone is locating and vandalizing plaster busts of a famed historical personage. Of course, Sherlock creators Steven Moffat and Mark Gatiss have had a little fun updating the original: Back when Conan Doyle first published it in Collier’s magazine in 1904, that story was titled The Adventures of the Six Napoleons. Check local listings.