There is the idiom "the dust settle(s)" which is used to indicate that after an argument or big change, the situation becomes calmer. The question is that why the verb "settle" varies in different structures? Please have a look on the following sentences:
- Let the dust settle!
- When the dust settle's'...
- We should let the dust settle from the recent scandal before we make any major policy decisions.
- We should only start painting when the dust settles after construction is finished.