Is the statement simply a summary of the plot or some aspect of the plot? In your critical writing, you are to assume that your reader has a working knowledge of the text in question plot summary of any kind is unnecessary. For example, to say that
"In The Red Badge of Courage, Henry Fleming's initial enthusiasm for a war quickly dissipates with his first battle experience"
doesn't tell us anything about the text that we don't already know. Such an observation may serve to support a thesis statement, but does not suffice as a thesis statement, but does not suffice as a thesis statement itself.