Six years after Elinor Donahue left her Mayberry gig at Walker’s Drugstore on The Andy Griffith Show, she transformed herself entirely from small-town sweetheart to shimmering alien entity on Star Trek.

The 1967 episode was called “Metamorphosis,” and it called on Donahue to play two roles at once: 1) a “really tough broad” on the Enterprise named Commander Nancy Hedford, and 2) an energized cloud that borrows Hedford’s human form after falling in love with a Federation diplomat (Glenn Corbett) the cloud kidnapped. It was an intense role, but Donahue told the Archive of American Television that she didn’t even have to audition.

"Gene Roddenberry called me at home and had called [Father Knows Best producer] Harry [Ackerman] at the office to ask if he could call me. And said this was the first season of a new show Star Trek and explained to me what it was. And would I like to be in it?"

Donahue didn’t hesitate: "I said sure!"

She had no idea she just committed herself to a month-and-a-half on set, due to cosmic mishaps that extended her time working on the series, despite only appearing in one episode.

As Donahue tells it, "I was on [Star Trek] for quite a while because something happened to the film midway through shooting… and there was some kind of jagged thing running through all the film, and they’d already torn the set down, so they had to completely rebuild the set, but they were already shooting something else on that same stage, so they couldn’t rebuild the set until they were finished what they were shooting now."

According to Donahue, these staging issues turned her guest role into something more like a job, but she didn’t mind, because she said being around the cast and crew was enjoyable.

Donahue said of Shatner, "He was fun. He was tough. Very tough." Then continued, "Leonard Nimoy was fun. I loved watching him have his ears put on in the morning. All the guys were terrific."

Unfortunately, shooting her scenes stretched on so long that during that period, Donahue said she fell so sick that she lost 10 pounds. This might not seem like that big of a deal, but because her costume had been form-fitting, Donahue said it made a noticeable difference. She told Archive:

"It was like a job. I was on it for like a month-and-a-half. In the meantime, I had caught pneumonia, lost 10 pounds, and when I came back, because I played two characters — I was Commander Hedford and then I was this pretty kind of blob — and when the blob becomes a human form, I’m it. And I was wearing sort of the costume that Commander Hedford had, but minus the jacket, and I had lost so much weight that the top was hanging out here on me, and so they had this big, blue, fluffy thing that they put around my neck and down my arms to cover up that I was so skinny."

Next time you watch the episode, note the flowy scarf that she wears during what Donahue described as the scene that turned out to be one of her best learning moments on the set of Star Trek: "It was Harry Ackerman’s most favorite thing that I ever did," Donahue said, describing her character’s speech toward the end of the episode, which found the actress in a position she’d never found herself in before.

According to Donahue, the cinematographer Gerald Perry Finnerman placed her in the scene up against the tree behind her in the speech. Next, he carefully lit the shot, then gave her a very specific direction: "He said, '…just say the speech. Don’t move.'"

Donahue said she responded, "But I have to move!"

This did not budge Finnerman one bit, so the actress had to adjust. Donahue said, "It was a wonderful acting exercise, because I had to do it all with my eyes. No bobbing of the head. No tricks. And I was very happy about it." (Watch the scene in the video at the top of this post and maybe consider how Raymond Burr's Perry Mason might relate.)

Her performance is magnetic and it makes the episode’s conclusion that much more tragic, leading us to a touching ending where what Donahue described as the "ectoplasm thing that was very loving" reveals it has sacrificed itself.

In Donahue's final scene with Corbett, his diplomat character asks her, flabbergasted, "You mean, you gave up everything to be human?"

The shimmering quality of the cloud remains in Donahue’s eyes as she insists it was worth it because, "The joy of this hour, I am pleased."

It’s fair to say the same for the actress on her surprisingly extended experience at the dramatic heart of this classic Star Trek episode.