It may be mixing metaphors to speak of game plan , backbone , and glue in the same breath. The point is that all the parts of an essay must fit and stick together. In other words, an essay must boast the virtues of unity and coherence .
Unity is the backbone of the essay.
One way to check for unity to make sure that all the sentences in a paragraph support that paragraph's topic sentence and that all the topic sentences in an essay support that essay's thesis. It is even helpful if you can find the gist of each topic sentence in the thesis statement's sneak preview. I often tell my students that I can usually cast judgment on an essay's unity by glancing quickly at its thesis and topic sentences. Of course, more advanced writing may reduce or de-emphasize this elaborate superstructure. But it never hurts to keep that superstructure in place in the early stages of writing.