In Long Bright River, Amanda Seyfried Serves and Protects

For Amanda Seyfried, the first day on set for “Long Bright River,” a limited series for Peacock, was awful.She stood under the lights in a mock-up of a police morgue, in her patrol cop uniform, unsure how to move or speak.“Every first day of work, I never know what the [expletive] I’m doing,” she told me later.Seyfried overprepares for most roles.

She researches; she memorizes; she asks question after question.But then suddenly she’s on a soundstage somewhere, with the lights blazing and the cameras pointed at her face, and the terror rushes in.

If she has an acting process, she said, “it’s all based on the fear that I’m not going to be good enough.”Seyfried, 39, was speaking on an icy February morning.We’d met for a late breakfast at a cafe on the Upper West Side of Manhattan, near where Seyfried keeps an apartment.

(She and her husband, the actor Thomas Sadoski, and their two children, spend most of their time on a farm upstate.) She was in town to shoot a Paul Feig movie, “The Housemaid,” and to promote “Long Bright River,” a moody eight-episode suspense series that premieres on March 13.She had recently wrapped “Ann Lee,” a historical musical by Mona Fastvold.Does this sound like a lot? It was.

“I think I’m falling apart,” Seyfried said as she looked at the menu.She had recently injured her back on “The Housemaid” and was taking muscle relaxants.“I’m fine now,” she said.

“I mean, I’m not.I’m struggling, but I’m walking.”Seyfried has been in the business for more than two decades, and has moved, gradually, from comedy (“Mean Girls”) and romance (“Mamma Mia”) to more complex roles.

Her performance as the actress Marion Davies in the Netflix film “Mank” earned her an Oscar nomination, and she won an Emmy for her portrayal of the convicted fraudster Elizabeth Holmes in the Hulu mini-series, “The Dropout.” With those roles and those accolades secure, she has finally been recognized as a...