They've checked every possible channel. The Air Ministry are positive that no papers are missing that would be of any possible use to spies.
8 seconds sound clip from the The 39 Steps (1937) classic radio play.
You can hear this line at 00:47:12 in the radio play.
Quote context
[...]
- Bring me a bottle of ale, will you?
- Did you think I was never coming?
- Not exactly, but I was getting nervous waiting.
- Well, what happened? Did you go to Scotland Yard?
- Yes.
- Well?
- Prepare yourself for a shock.
- But that's incredible. Are you sure?
- Well, that's exactly what they said.
- I don't know what to make of it.
- I think you've been tricked.
- Well, it certainly is all very bewildering.
- Oh, I'm sorry, really I am. Look, I think you better go now.
- Oh, any place. Leave the country.
- You?
- Oh, I know it sounds funny, but somehow I couldn't bear the thought of them catching you again.
[...]