Opera detective
Operas have such a reputation for bad plotting that some people overconfidently nitpick them. Beethoven's Fidelio deserves some of the nitpicks it gets. Leonore infiltrates the prison disguised as a young man, and she's so successful that she gets engaged to the jailer's daughter rather than blow her cover. But there's at least one complaint that isn't justified by a careful reading. (Should I put up a spoiler alert? For an opera?)
As Leonore holds Pizarro at gunpoint down in the dungeon, a trumpet announces the arrival of Don Fernando. A few seconds later it sounds again, louder. Nitpickers point out that the trumpet shouldn't have moved, and there's no mention of a relay. But it actually makes sense. The exact stage direction is "Man hört die Trompete stärker," the trumpet is heard more strongly. Immediately after this second trumpet call, Jaquino appears at the top of the stairs and announces the Minister's arrival.
So it's very simple. The door was opened before the second trumpet call.
As Leonore holds Pizarro at gunpoint down in the dungeon, a trumpet announces the arrival of Don Fernando. A few seconds later it sounds again, louder. Nitpickers point out that the trumpet shouldn't have moved, and there's no mention of a relay. But it actually makes sense. The exact stage direction is "Man hört die Trompete stärker," the trumpet is heard more strongly. Immediately after this second trumpet call, Jaquino appears at the top of the stairs and announces the Minister's arrival.
So it's very simple. The door was opened before the second trumpet call.