THE SERIES: “The Defenders”

WHEN, WHERE: Streaming now on Netflix

WHAT IT’S ABOUT: A new treachery stalks New York in the form of Alexandra Reid (Sigourney Weaver), prompting Jessica Jones (Krysten Ritter), Luke Cage (Mike Colter), Matt Murdock/Daredevil (Charlie Cox) and Danny Rand/Iron Fist (Finn Jones) to join forces. When last we saw Jessica, she had slain the evil Kilgrave (David Tennant); Luke had saved Harlem with the help of Claire (Rosario Dawson), but was sent back to Seagate prison; Danny/Fist killed Harold Meachum (David Wenham) then headed back to Kunlun with Colleen Wing (Jessica Henwick); and ninjas from the Hand had killed Elektra Natchios (Élodie Yung), sending Matt into a depression. The eight-episode “Defenders” picks up a month or so after that.

MY SAY: As a newcomer to the Marvel multiverse, Alexandra may be mysterious but not so much the actress playing her. We’ve known and loved Sigourney Weaver for more than 40 years. She has been canonized as the greatest female action hero in movie history, as an avenger both cerebral and deadly. But while we thought we knew them well, “Alien’s” Ripley and “Avatar’s” Grace Augustine were essentially unknowable at their core. Too shrewd to yield their secrets, too smart to need to, they were a little more brainy than bad-ass. That was part of their allure and mystery.

Which brings us to Alexandra. Viewers first meet her as the woman in haute couture white. Her fashion tastes range from ivory white to bright white, offset with black lines or gold lamé pants. Alexandra is unknowable, too.

Naturally, she has killer moves.

That Weaver is the best part of “The Defenders” — at least during the first four episodes provided for review — is about the only mystery we can clear up for you here. She emphatically is, while the rest of these four hours is devoted to taking care of necessary business. Rarely exhilarating, consistently workmanlike, “The Defenders” at its outset is occasionally hamstrung by five separate story lines that must converge, but how they ultimately do feels more arbitrary than seamless. You can almost hear the wheels of this hydra-headed story grind, then click, into place.

Because it’s a small world after all — or the island of Manhattan is small by comparison — Danny crosses paths with Luke one dark night, both following leads, then Jessica makes Matt’s acquaintance. Still aching from Elektra’s death, he’s done with Daredevil forever, or so he’s deceived himself into thinking. Jessica is done with the hero business, too, and almost seems to mean it. They’re on the same page, while Fisty and Luke, as instant antagonists, aren’t even in the same book.

But something has to yoke them all together, and sweep away the doubts. Something has to make them understand that the fate of the world hangs in the balance; that the glorious city on the Hudson is imperiled; that matters of the heart, petty grievances, and individual ambitions must be swept aside in service of some greater destiny and glory.

A few old friends return to help, including “Luke Cage” private investigator Misty Knight (Simone Missick) and Stick (Scott Glenn), Matt’s mentor and adversary of that dastardly ancient Ninja order, The Hand.

But it’s Alexandra who’s key to everything. Just powerful, dangerous and mysterious enough, she’s the reason the Defenders can find common cause. Meanwhile, a much-anticipated series and beloved franchise has already found an indispensable newcomer.

BOTTOM LINE: A little clunky at times, but otherwise all is well here, thanks especially to Alexandra.