Four short lines, and almost every one is uncertain. The poem opens with two questions that have no question marks: who to trust or listen to, where to consult. The speaker seems lost, in a place where it isn't clear whom to believe or where advice might safely be found. The title, "Covert," adds to that sense of secrecy and hiding.
Then comes the strange, striking image of prisoners who "whisper publicly." That phrase is a contradiction, since a whisper is meant to be private, yet here it is done in the open. Judging by the wording, the speaker may be describing people who are watched or confined, for whom even quiet talk is shared and exposed. The final simile, "like water in the night," makes the whispers soft, steady, and hard to pin down, a sound you hear without being able to grasp it.
The mood is hushed, wary, and a little eerie. There is no answer, only listening in the dark.