The plot -- like most -- is impossible to recount; the very existence of such a ridiculous plot is just one of the many wonderful artifices that make opera, like good cooking, a cultural activity worthy of writing about. Things don't happen this way in real life, we might well say. And a good thing, too. It's the differences from reality that matter. One of those differences is in the magical way opera has of stopping time: those freeze-time moments when nothing happens while everything (under the surface) sorts and re-sorts itself.
One utterly ridiculous man, Baron Ochs von Lerchenau, is the nominal center; at least, he likes to think he is. It's a great bass part, comic, lyrical, abusive, egotistical. At the end of Act Two, exhausted, he stops chasing the chambermaid and bossing the bourgoisie long enough to have a moment of quiet. An old song pops into his head, and, it being opera, he sings it. "Ohne mich..." -- "without me." It's ego, but sweet, a country-type waltz that is the right place for this bumpkin to be. For a little while, time stops.
Romantic music always stops time when people fall in love. Here (again, the plot is absurd), a young aristocrat, Octavian, presents a young woman, Sophie, a rose on behalf of his boorish cousin Ochs. Never mind why. What matters is: first, Octavian is a boy, but he is sung by a woman, and dresses as a woman twice in the opera; and second, the two fall in love during the presentation of the rose. Here's a concert performance of the scene; at about 2:00, you'll catch what I'm talking about. Notice the beautiful high chords in the orchestra, like stars twinkling on a New Year's night. And the incredibly beautiful high notes of the two women, holding time away...
The opera not only stops time at these key moments, it embeds the stopping of time in the fabric of the story, the characters, and the music. At the real center of the opera -- Baron Ochs only thinks he's the center -- is a beautiful and privileged woman (the Marschallin), for whom time is running out. "You have made me an old woman," she says to her hairdresser; she knows, though, it's not he who has aged her. It is she who most articulates the theme of the opera: while we can make moments of beauty and love, time will always win out.
(In tragedy, we can't get to the end soon enough: death is better than life; but in comedy, the happy endings are often saddened by the difficulty of maintaining equilibrium: "The rain, it raineth every day.")
At the end of Act One, the Marschallin sings, "Time is a strange thing," and recounts to her young lover how sometimes she wakes in the middle of the night and goes about the house stopping all the clocks. You'll hear the clocks striking (13 times). . .
Strauss's Vienna in the Rosenkavalier is of the ancien regime, with wigs and lace. But it is also the Vienna of Freud: "If youth knew; if age could."
