Kate Mulgrew achieves a kind of alchemy with her performance in ``Tea at Five.''

The actress best known for commanding the crew in ``Star Trek: Voyager'' embodies the actress Katharine Hepburn, with all her glorious idiosyncrasies, at two extraordinarily different moments in her life, and she does it with an ease that is remarkable.

Playwright Matthew Lombardo has chosen to spotlight the legendary film star at two defining points in Hepburn's life. In Act I, we meet the 31-year-old just as she's retreated from Hollywood to her family's estate in the Fenwick section of Old Saybrook, Conn., (where Hepburn still lives). She's mischievous and arrogant, sometimes fearful the studio's label of ``box office poison'' will stick, sometimes determined to defy the barbarians at her gate.

As she nervously awaits a phone call from her agent telling her if she's gotten the coveted role of Scarlet O'Hara in ``Gone with the Wind,'' she tells us of her struggles toward stardom. Lombardo cleverly links several famous bits, most notably her performance in the play, ``The Lake,'' which contained the oft-quoted line, ``The calla lilies are in bloom again,'' and prompted Dorothy Parker's famous quip that ``Katharine Hepburn ran the gamut of emotions from A to B.''

Mulgrew paces the room like a caged animal, lounging, posing, flinging out her arms and tossing her legs across furniture. Every moment is a performance, even in the quiet of the Fenwick home. But beneath the bravado, cracks are beginning to show, and the strain of keeping up appearances - the scheduled tea at five of the title - is taking a toll. Mulgrew offers aching glimpses into the strength Hepburn must summon to go on.

But every time Lombardo tries to dig underneath the familiar tales and get behind the familiar Hepburn poses, he stumbles. Just as Hepburn admits her first failure was as a wife (her only marriage ended quickly in divorce), and says she ``went back to the theater without any caretaking responsibilities,'' she then dismisses it with a simple, ``we actors are an odd lot,'' and Lombardo shifts back to safer turf.

In Act II, Mulgrew makes an astonishing transformation, appearing as the 76-year-old actress who is back at Fenwick recovering from a broken ankle as a result of a car accident. Her look has been transformed from the stylish pantsuit and red-headed pageboy cut, to Hepburn's turtleneck and blue workshirt and pants with gray hair swept up in a bun and her tremors from Parkinson's disease.

This Kate has mellowed considerably and is more philosophical about her career and the choices she made. She talks about the isolation of her grief when her brother Tom committed suicide, and her determination to make her apparently cold father proud. But again, just as we get near what motivated Hepburn's stubborn drive, Lombardo veers to a story about Stephen Sondheim.

From there, Lombardo makes another sharp turn to her 27-year relationship with Spencer Tracy, a man she describes as a bully, who's appeal lay in his need for her. To leave him, she says, was to choose to be alone.

Somehow, that's not enough, and it's disappointing that such a terrific performance must work with such slight material. Despite Kate Mulgrew's luminous performance, the woman behind the marquee name of Katharine Hepburn remains elusive.