Just as good as any

Synopsis: La Bohème

Act I
Lucia, a consumptive seamstress called Mimi, comes upstairs to get a light from the poet Rodolfo. They fall in love.

Act II
Everyone except Alcindoro has a good time at the Café Momus on Christmas Eve.

Act III
Mimi and Rodolfo don't separate.

Act IV
Mimi dies.

Other curious synopses I've found so far: La Traviata and Madama Butterfly. The full list of operas are here. Many external links are no longer working (paging whoever-- stop downloading Gruberova pirates and go back to work, please), but it's worth a half-hour of indoor amusement on this humid Monday afternoon.