Danger in case one sounds unsure (5)
I believe the answer is:
peril
'danger' is the definition.
(peril is a kind of danger)
'case one sounds unsure' is the wordplay.
I cannot really see how this works, but
'one' could be 'er' (I've seen this in other clues) and 'er' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for peril that I've seen before include "Danger of serious kind" , "Exposure to harm" , "Danger, jeopardy" , "risk" , "Immediate danger" .)