Meanings of mislaid letter in English

But this evening I hunted through its pockets looking for a mislaid letter, and I found my hypodermic syringe.

You will remember that there was a mislaid letter whose possession had become a matter of supreme importance to a certain great person in Russia.

On this desk the many papers before the President are methodically arranged, and he never has to waste time in hunting for mislaid letters.