The television event of the season, if not the entire year, “Downton Abbey, Season 2” debuts on “Masterpiece” (8 p.m., PBS). An “Upstairs Downstairs” for the 21st century that far surpasses the recent remake of that “Masterpiece” phenomenon, “Downton” returns three years into World War I, as the grim death toll touches members of every class.

The backdrop of war and social upheaval puts a historical gloss on a classic and addictive melodrama, a tale of a major estate with a contested heir, of loves misguided, misdirected and contrived. Everyone at Downton, it seems, is trying to manipulate somebody else into doing their bidding, and the string pulling runs up and down the hierarchy.

Once again, Maggie Smith presides with a regal hauteur combined with an almost childlike frankness. She always states her mind and gets nearly all of the best lines.

”Downton” is not perfect. Too often Lord Grantham (Hugh Bonneville) is reduced to time-marking platitudes like, “We’re witnessing the end of an era.” Lady Grantham (Elizabeth McGovern) appears in an unvarying array of reaction shots as her icy blue eyes widen in disdain, shock, horror or amusement. A subplot about a daughter’s love for a rebellious chauffeur appears to go nowhere, and takes its sweet time getting there.

But at the end of the day (or at least until “Downton” ends on Feb. 19), nobody will much care about such quibbles. “Downton” is best enjoyed for the gorgeous locations, beautiful sets and onslaught of period wardrobe changes that must have required a sweatshop of nimble seamstresses. “Downton” is a lock for every costume award at the Emmys.

More than 13 million viewers watched the first “Downton,” and a million more streamed it online. In its native U.K., “Downton” is the most popular and acclaimed miniseries since “Brideshead Revisited” debuted in 1981. It’s not because “Downton” is the best acted, most cleverly scripted, most profound story ever. It’s because it combines great, overlapping human-interest stories against a backdrop of historical heartbreak and staggering beauty, art-directed to perfection.

In a medium where many programs run too many seasons and most movies are at least an hour too long, “Downton” is one of those rare offerings — a series you hope never ends.

Tonight’s other highlights

• Scheduled on “60 Minutes” (6 p.m., CBS): stem cell research, brothers in arms, the allure of truffles.

• Scheduled on “Dateline” (7 p.m., NBC): Jennifer Hudson; a honeymoon cruise ends in mystery.

• Homer becomes a radio talk show host and Republican kingmaker on “The Simpsons” (7 p.m., Fox). Ted Nugent guest-voices.

• Emma throws her hat into the ring on “Once Upon a Time” (7 p.m., ABC).

• A former client lodges serious charges on “The Good Wife” (8 p.m., CBS).

• Bree is at the end of her rope on “Desperate Housewives” (8 p.m., ABC).

• Florida guys hunt giant reptiles in the latest backwoods docu-comedy “Gator Boys” (8 p.m., Animal Planet).