Not until that secret is learned can another expedition expect to return.
3 seconds sound clip from the 20 Million Miles to Earth (1957) movie soundboard.
You can hear this line at 00:30:44.661 in the Blu-ray version of the movie.
Quote context
[...]
- And Doctor Sharman, the chief scientist, also became fatally ill.
- He died here after the ship crashed.
- Fascinating. Horrible, but fascinating.
- Now, on that ship was a particular sealed metal container.
- In it is an unborn specimen of the animal life on the planet. We've got to find it.
- Our task is to discover in what physiological way life is able to survive and to flourish there.
- Not until that secret is learned can another expedition expect to return.
- I'm at your disposal, general. In what way may I assist you?
- We need divers, several divers to descend to the wreck to search for the specimen.
- They will be here in the morning.
- Don't you want me to drive for a while?
- No. No, cara, non sono stanco, grazie.
[...]