Here in full, the Wikipedia plot summary of La Vie Parisienne (1866).
Act 1
The story begins at the railway station, where the employees boast of all the wonderful places in France. Soon, Baron and Baroness Gondremarck arrive from frozen Stockholm for a Parisian holiday and ask tour guide Joseph Partout to show them the city’s glittering night life. Finally, Pompa di Matadores, a Brazilian millionaire, arrives to spend a fortune in the capital.
Act 2
Métella, a demi-mondaine with a heart of gold, reads a letter from Baron Gondremarck’s friend, Baron Frascata, asking her to give Gondremarck the same pleasure she once had given him.
Act 3
At a party, the guests vow to make their pleasure long lasting as they eye one another, waiting to see who will make the first move. Bobinet rises to greet the crowd with a drinking song. The champagne flows and Baron Gondremarck (and everyone else) gets drunk. The party turns into a wild, sensual debauch.
Act 4
The Brazilian millionaire is offering a masked ball. Métella, anxious to win back Gardefeu, is in league with the Baroness, who wants to extricate her husband from the perils of Parisian life. The Brazilian and Gabrielle, the pretty glover, discover the virtues of love at first sight. All ends happily.
So: in Act 1, the characters assemble and – the curtain falls. In Act 2, Métella reads a letter, perhaps silently, broodingly, facing upstage. In Act 3, however, all hell breaks loose. I very desperately want to see this operetta.