THEATER REVIEW : Prisoner in the Shadows of East Berlin : The Whitefire offers an emotionally gripping tale of a suspected spy and her questioner in its production of ‘Days and Nights Within.’

Elsa Faber made a mistake. She flew to East Berlin in 1950 to locate a friend. She was taken in for questioning as a West German spy, accused of recruiting her friend and others for espionage work. For more than a year and a half, her Interrogator tries to make her divulge names and more names.

“Days and Nights Within,” Ellen McLaughlin’s chamber drama at the Whitefire Theatre, is just one more entry in the interrogation genre, but is distinguished by the playwright’s insightful approach. For the entire period of Elsa’s imprisonment, her only contact is the Interrogator, and they play an intricate game of cat and mouse. The game volleys widely in its view of Elsa’s inner strength and the questioner’s infinite patience.

It is a difficult piece, with many colors in varying shades, from outright emotional despair on both parts to Elsa’s dream images of the relationship. Elsa’s evolving mental dependence on her torturer, and his cleverly veiled, gradually awakening desire are delicate and easy to unbalance.

Director Chris Fields has that balance in hand, along with the kaleidoscopic dramatic tones that flash from scene to scene, but a bit more gut power would be helpful at times, a breaking loose from the slow build that Fields has carefully created.

It would also help if the two actors maintained a richer vocal energy, even in their more intimate moments. Both Julia Mueller as Elsa and Paul Perri as the Interrogator are deep into the intricacies of their characters, but there are times when they seem to hold back, rationing their strength too much for even a small theater space. We see inside Elsa and her foe, but at times the light shines less brightly than it could.

Emanuel Treson’s bare-bones set is just right for the spareness of the piece, and his lighting helps to move the drama as much as the performances. Bob Murphy’s sound is excellent, as are Jim Wood’s costumes, particularly Elsa’s prison rags, all that remain to remind her that she is a human being.

WHERE AND WHEN

* What: “Days and Nights Within.”

* Where: Whitefire Theatre, 13500 Ventura Blvd., Sherman Oaks.

* When: 8 p.m. Thursdays through Saturdays, 7 p.m. Sundays. Ends June 27.

* Price: $10.

* Call: (213) 957-4697.