Roz takes a week of vacation, leaving Frasier in need of a temporary producer. He is reluctant to turn to his usual substitute because the man has a speech impediment. Frasier decides to use a broadcasting student, and settles on Mary Thomas, a woman who chose radio as her career after taking some night school courses. Mary is initially shy and afraid to speak on the air, but Frasier urges her to contribute. She soon takes over, constantly interrupting Frasier and contradicting his advice with her own no-nonsense approach. She annoys Frasier further by referring to herself as "Dr. Mary." Frasier insists that he hasn't asked her to stop because she is a beginner and he doesn't want to squash her enthusiasm. Martin feels that the real reason is that Mary is black and Frasier is afraid that she will think he is racist. After Mary ends up as his co-host (and won't allow him a word in edgewise), Frasier finally tells her how he really feels about her performance. Mary is understanding, and reveals that she has gotten her own show on another station. Meanwhile, Niles inadvertently injures Daphne while trying to demonstrate his kickboxing skills. He takes over her duties while she recuperates, and Martin and Daphne take advantage of his guilt.