He had put them on after supper, just before going on watch; the substitute assistant had seen him do that, also.

Therefore, the clay must have been acquired sometime during the evening or night just past.

And certainly there was no clay at the "top of the lighthouse," or anywhere in the neighborhood except at one spot--the salt marsh at the inner end of the cove.

Seth must have visited that marsh in the nighttime.

But why?
And, if he had done so, why did he not mention the fact?
And, now that the helper thought of it, why had he been so agitated at the casual remark concerning wading?
What was he up to?
Now that the Daisy M.and story of the wife were no longer secrets, what had Seth Atkins to conceal?
Brown thought and guessed and surmised, but guesses and surmises were fruitless.