Nick Briggs for The New York Times

"Downton Abbey" returns to American television Sunday with Tom Cullen as a suitor courting the widowed Lady Mary, played by Michelle Dockery.

NEWBURY, England — We have raged against fate and come through our stages of grief. We have accepted that no matter how much we miss him — his limpid blue eyes, his good sense in marrying Lady Mary after his tiresome fiancée finally succumbed to the flu — Matthew Crawley is never coming back. He is dead, having been hit by a truck while driving inattentively in the waning moments of last season on "Downton Abbey."

The surviving characters have been coming to grips with that jarring development, too, a process that has taken place off screen, thankfully, as sustained mourning is not much fun to watch. The fourth "Downton" season, starting Sunday on "Masterpiece" on PBS, begins six months after the crash, with the household — Lord and Lady Grantham, their two surviving daughters, Mary and Edith, and the servants below stairs — dusting itself off from this most wrenching of calamities and getting on with the business of living. Naturally, some characters are faring better than others.

"If there's a theme to the fourth season, it's how Mary will rebuild her life," said Gareth Neame, a "Downton" executive producer. It was April, and Mr. Neame was sitting, somewhat incongruously, in a modern-day office at Highclere Castle, the real Hampshire estate here that stands in for the fictional Downton Abbey for some scenes (others, including bedroom and kitchen scenes, are filmed at Ealing Studios in West London). The house was littered with props and film equipment. Actors flitted around in period attire.

Virtually no one (except Dan Stevens himself) wanted Dan Stevens, the dreamy English actor who played the popular Matthew, to leave the cast. But his decision to seek his acting fortune elsewhere meant he had to be killed off, and the show runners decided to turn the problem — Lady Mary's sudden widowhood — into a dramatic opportunity. In truth, it may have happened at a good time, providing a chance to breathe new life into a show that has increased its audience size at a surprising rate even as critics and some viewers grouse that its narrative lines are not as exciting as they once were. Also, happily married is a boring state to depict on screen, especially when the love scenes involve a 1920s husband who wears pajamas in the bedroom.

"Once a young couple get married, there tends to be a dramatic lull," Mr. Neame said. "The idea of numerous suitors arriving, interested in Lady Mary, is very exciting."

There will be other plot developments, too. Among a handful of new characters will be the show's first black character, a jazz singer played by Gary Carr. The redoubtable Shirley MacLaine will return at the end of the season, playing Lady Grantham's feisty American mother, and will be joined this time by her feisty American son, played by Paul Giamatti. Lady Edith, jilted at the altar by her weedy beau, will have some interesting escapades, as she branches out in unconventional ways, both personally and professionally.

Meanwhile, Lord Grantham will have to adjust to the changing times while finding a way to pay the crippling death duties brought on by Matthew's demise; Branson, the chauffeur who married into the family and has been promoted to estate manager, will continue negotiating his uneasy transition from downstairs to upstairs; a beloved below-stairs cast member will be the victim of a shocking crime that will be followed by an incident that may not be murder but will be suspenseful. And Carson, the butler, will go on being Carson.

"Poor old Carson," said the actor who plays him, Jim Carter, speaking in his trailer — one of dozens parked down the hill from the castle — during the day's lunch break. "He's worn the same clothes, and poured the same wine, for four years." As the butler, his job, he said, is to provide a bulwark of stability for the household, no matter what. "He's not allowed to have much of a social life. The nation demands!" said Mr. Carter, whose hair looked unruly and un-Carsonesque. ("I come in looking like a haystack, and they put something on it to make it go quite solid," he said.)

Back in the house, the cast was rehearsing a scene featuring a discussion of the whereabouts of Lady Edith, who was apparently at an unknown location in London. Any conversation with Maggie Smith, as Lord Grantham's mother, is bound to feature some waspish remarks, and in this one, the actress — in civilian attire with short hair and bluejeans — was reciting a line in which her character dismisses the notion that Edith might have some exciting things going on: "Edith's about as mysterious as a bucket."