Present-tense narrative is common in jokes (A priest, a minister, and a rabbi walk into a bar...) and in some folktale traditions, and it has become something of a mannerism in some contemporary novels. In this case, however, the present tense is employed because the speaker is not actually telling the story but re-telling it and summarizing its key events. As I wrote in another context here
The convention in English for at least five hundred years has been that when you are describing an existing story/novel/drama/opera you employ the present tense, as if the story were unfolding before your eyes.
Plot summaries in programs and critical works are almost always cast in the 'historical present'.