This sentence: "Es soll dein Shaden nicht sein." Has been haunting me :)
Since this came for a children's version and a translation, I first went back to the adult version (in German), and tried to find the intended meaning in the story that lead to this sentence.
I then went back to the original English, and I now have a new theory: In the original story, the Captain IS very concerned about the one-legged man. He even pays the boy (Jim) to keep his eye out for the one-legged man.
So the best meaning seems to be:
"It would be a shame for you if you didn't (inform me)."
To close the par between the desired meaning (above) and the German sentence for the children's book, I'll make it this:
"It should, for you, be a shame (if) not (you inform me)."
"Es soll dein [sein] Shaden nicht sein."
I would appreciate any comments which can help clarify how "nicht" can do so much work: It seems to encompass both the conditional idea of "if/when", and at least one extra verb (either "you do" or "you (not) inform me".
(Final thought: perhaps it's the "soll" that accomplishes the constitutionality which I seem to be seeking.)