A few minutes into the long-awaited "Upstairs Downstairs" sequel, launching Sunday on PBS' "Masterpiece," the new mistress of 165 Eaton Place walks into an employment agency for domestic staff. As the owner of the agency places a tea service on her desk opposite the new client, the camera moves upward to the face of Rose Buck, the former parlor maid at Eaton Place and arguably one of the most beloved characters in TV history.

The moment they first see Rose, played by series co-creator Jean Marsh, many viewers may feel as if they are reuniting with a beloved member of the family, absent from home far too long. But it also points up the challenge of doing a sequel to a wildly popular TV series 40 years after it premiered on Britain's ITV and three years later on what was then called "Masterpiece Theatre": How to create a sequel to appeal both to those who watched every episode back in the '70s, as well as to newbies who wouldn't have the background to just jump into the epic (unless they happened to have bought Acorn Media's exquisite 40th-anniversary DVD set).

Producer Nikki Wilson and writer Heidi Thomas have solved the problem rather deftly with the three new "Upstairs Downstairs" episodes (9 p.m. EDT Sunday, and April 17 and 24). While the original 68 shows took the wealthy Bellamy family and their household staff from 1903 to 1930, the sequel begins in 1936 as a young diplomat, Sir Hallam Holland (Ed Stoppard), and his wife, Lady Agnes (Keeley Hawes), move into the long-abandoned house on Eaton Place that is badly in need of both renovation and a household staff.

What made the original show special -- the deceptive simplicity of its plot -- informs the sequel as well. The house, which may have been owned by the Bellamys but belonged just as much to the downstairs staff, was a microcosm of sorts, albeit one that traded on the surface at least on the English fascination with class differences and interrelationships. Within the world of Eaton place, then and now, swirl passion, intrigue, deception, spite, jealousy, death, betrayal and forgiveness.

As self-contained as 165 Eaton Place seemed in the original series and in the sequel, human history was proceeding apace beyond its elegant portico. In the first series, England was awakening from the Victorian era and heading toward World War I. In the sequel, King George is dying and his son is forced to choose between ruling the Commonwealth and marrying "the woman I love," the American Wallis Simpson (Emma Clifford). The abdication of Edward VIII disturbs Hallam's longtime friend, the Duke of Kent (Blake Ritson), younger brother to both Edward VIII and the future King George VI.

But once again, England is heading toward war, as Hitler amasses power on the continent and Sir Oswald Mosley's British Union of Fascists promotes German sympathies on the home front. Political reality hits very close to home when Agnes' sister, Persie (Claire Foy), takes up with chauffeur Harry Spargo (Neil Jackson) and finds herself naively drawn toward his pro-Mosley politics. Meanwhile, the Hollands have hired a young maid who turns out to be a Jewish refugee.

The performances are precise and beautifully detailed, as are the characterizations in Thomas' script. Fans of the original series will see certain echoes in some of the characters in the sequel, but the echoes are faint enough to allow us our memories of, among so many others, Rachel Gurney and David Langton as the Bellamys, Angela Baddeley as the cook and Gordon Jackson as Hudson, who was so much more than just the butler.

Although all the characters except Rose are new in the sequel, one merits special mention, and that is the co-creator of the series, the great Dame Eileen Atkins, who was supposed to play another parlor maid in the show but was tied up with a play in London when the series finally went before the cameras.

Belatedly, Atkins makes her appearance here as the formidable Lady Maud Holland, Hallam's mother. After years of globe-hopping, she swans into her son's refurbished townhouse with her Sikh manservant, Mr. Amanjit (Art Malik), her pet monkey and a singular sense of entitlement. In the case of the actress, if not the character, it's very much deserved.