So, you can kind of add up the pieces, like a puzzle, he drew this man which was a criminal and then he somehow ended up at his workshop where he was engraving James’s name and date of birth and date of death on there, the date of death happened to be that same day, then the uncanny man suggests that he stay over until 12 o 'clock as a safety precaution, then at the end of the story there’s a sudden turn of events where the character explains how the heat was enough to drive a man mad which could’ve been what happened and maybe the gravestone went to use with the appropriate information already on it afterall.
There are various methods with which you can create suspense in a story. In August Heat the author has it down to a science, in fact he manages to use all four methods in just one short story. W.F. Harvey manipulated foreshadowing, withholding information, placing a character in a dangerous situation in which he must make a choice, and a sudden change in a character’s situation in a great way.
“The word suspense is related to the word suspended. When a story keeps us in suspense, we feel almost as if we are suspended in midair. We may even hold our breath without realizing it as we read on eagerly to find out how the story ends.” (Harvey, August Heat, pg