And actress Kate Mulgrew just doesn't know why.

"I get very emotional before I go out. I get very teary." She's not sure if it's
because doing a one-woman show about the legendary actress is "overwhelming" or if perhaps she feels such a desire to get it right for Hepburn. "I sit in my dressing room and I look at myself in the mirror and I think, 'Oh, my God, here we go again.'"

But then, Mulgrew says, "a kind of alchemy" happens.

"I get to the wings and I just want to throw up. I step onto the stage, and I
just want to fly."

Mulgrew's warm, throaty voice still holds a note of wonder about all she can't explain about her transformation into Hepburn in Matthew Lombardo's play "Tea at Five." It's the mystery of acting, she says, or maybe the mystery of why this combination of her and Hepburn has worked so well. Although she never met Hepburn, she feels as if she knows this "amazing" woman so well, and feels compelled to share her story by becoming her.

"It's so challenging. It's my little Mount Everest every night."

After creating the show at Hartford Stage in Connecticut, Mulgrew and director John Tillinger brought "Tea at Five" to the American Repertory Theatre in Cambridge in September 2002. It later played four months off-Broadway in New York City, where portraying the four-time Oscar-winning actress earned Mulgrew a 2003 Outer Critics Circle Award nomination for Outstanding Solo Performance and a 2003 Lucille Lortel Award nomination for Outstanding Actress. Mulgrew later performed the show in West Palm Beach and Phoenix and is due to go to Seattle next year.

For now, she's back in Boston, performing the play at the Shubert Theatre until Dec. 19.

Although the play itself has gotten mixed reviews, Mulgrew has won raves. Critic after critic talks about how she gets Hepburn's voice, accent, mannerisms and walk just right and how it often seems as if she is "channeling" the older actress. In Act 1, Mulgrew, 49, plays Hepburn at 31, coping with a string of box-office flops and hoping to win the lead in "Gone With the Wind." Instead, Hepburn would soon come back strong in 1940's "The Philadelphia Story."

In the second act of "Tea at Five," Hepburn is 76, her career is nearly finished and she reflects back on her long life, most touchingly the suicide of her beloved brother when she was 15 and her long romance with Spencer Tracy. Both acts take place at Fenwick, the Hepburn home in Connecticut, at teatime.

The transformation between the two Hepburns is a startling one that occurs quickly during intermission, and Mulgrew says the elderly version of the actress is the more physically demanding to play. Although she has consulted vocal coaches on less arduous ways to get Hepburn's tone and quaver from Parkinson's disease just right, she's had no luck and just tries to breathe right and save her voice on performance days.

"It's so wearing on my vocal cords," she says of the role. "I 'trick' my voice
in the second act. There's no other way to do it."

There has been some editing of the "Tea at Five" script since Mulgrew was in Cambridge, and that process continues. "I'm always trying to tighten it. I let go of anything that's the least questionable," she says. In one of several
frankly admiring moments in a chatty phone conversation, Mulgrew notes Hepburn "had such a life. As an actress, I can take a different journey every night, and I do."

But it's a journey Mulgrew fought against making for much of her life.

People had remarked on her resemblance to Hepburn - physically, her facial structure, her voice, her "strength of personality" - since Mulgrew was quite young. "Being an actress in my own right," she observes, "I resented it."

Mulgrew found success in 1975 by creating the fiercely independent Mary Ryan on the afternoon soap "Ryan's Hope" when she was barely 20. She went on to play a variety of roles on stage, TV and film, such as the title role in the TV series "Mrs. Columbo" and noted guest-starring roles on "Cheers" and "Murphy Brown." But Mulgrew is best known for her seven years as Starship Capt. Kathryn Janeway on TV's "Star Trek: Voyager," the first and only female captain in that long-running franchise.

Playwright Lombardo saw "Voyager" and was so reminded of Hepburn that he wrote "Tea at Five" expressly for Mulgrew. He got the script to her through a mutual friend just as she was looking for a return to the theater after "Voyager" ended in 2001. She was hesitant at first, but found the play "wonderfully written" and did extensive research on Hepburn. It was when she began "understanding" Hepburn, through the research and through playing her, that Mulgrew finally "fell in love" with the older actress.

But Mulgrew bridles at the idea that her uncanny portrayal is in any way an impersonation. "It never once occurred to me to impersonate," she says. "I came (at the role) from the inside out," the same way Hepburn took on a character.

Hepburn never saw Mulgrew playing her onstage, and Mulgrew says it's "possibly by degree a little less" difficult to do the part since Hepburn died in June, at age 95. "There's always a specter of (them) being there if they're alive," Mulgrew says of playing real-life people. "There's a sort of haunting thought about their being alive and watching you somehow." Now that Hepburn is gone, Mulgrew feels a responsibility to "watch" for her, and such imagined vigilance is maybe "what the getting teary is about. That must be what it's about."

Mulgrew had no expectation of segueing from playing such a strong, indelible character for seven years on TV, then playing another instantly identifiable character for years on a stage tour. She had thought "Tea at Five" might have a brief run, then it would be something she could play on and off. But this tour continues to be in demand.

She credits that success directly to "Star Trek" fans because "they're always
there." Some have seen the show 40 or 50 times and have become her friends; other fans have come from all over the world to the various productions.

"It's the most extraordinary allegiance I've ever experienced," she says, but
notes that the fandom has "moved beyond Janeway. They're honoring me as an actress."

She is also grateful for the "Star Trek" fans - mostly "remarkable" women - who have tirelessly worked to get other fans to her benefit shows for the
Alzheimer's Association, raising hundreds of thousands of dollars for
research.

That work is important to Mulgrew because her mother suffers from Alzheimer's disease. But that is just one of a string of tragedies that Mulgrew dealt with during a more than seven-month hiatus from playing Hepburn. During that time, Mulgrew's father died and her husband, Ohio politician Tim Hagan, had a heart attack and went through recovery.

When asked why she wanted to return to "Tea at Five" after the emotional turmoil of that break, Mulgrew answers that the play "takes me out of it. I don't have to deal with the sorrows of my own life. In a sense, it's an escape."

She talks briefly about the difficulty of bearing her mother's illness and how unfair it was for her husband to suffer with heart trouble, and then seems to shake herself out of the darker thoughts. "But life's not fair," Mulgrew says philosophically. "That's all the more reason to get on the stage."

"Alice Adams" (1935)

"The Lion in Winter" (1968)

"The African Queen" (1951)

When asked about her favorite moments in Hepburn's movies, Mulgrew delivers them - in Hepburn's voice:

"You liar...," as Rose, to Humphrey Bogart's Charlie, from "The African Queen" (1951)

"You're my knight in shining armor. Don't you forget it ..." as Ethel, to Henry Fonda's Norman, in "On Golden Pond" (1981)

"Oh, we're going to talk about me again, are we? Oh, goody," as Tracy Lord from "The Philadelphia Story" (1940)

When the title character of "Alice Adams" (1935) sits forlornly at a dance with wilted violets.

Any scenes with John Wayne in "Rooster Cogburn" (1975) - "because of their chemistry, the fun they were having."