Not bad. You obviously seem to have a good grasp on the English language, and I enjoyed where the story went. It is a bit repetitive in places, and the tense shift between the end of 4:20 and the middle of 4:27-from past to present, then back to past-was somewhat jarring; if it was intentional, I would try to write the entire section for 4:27 that way (to imply a sense of urgency on both the professor and the student's parts), and switch 4:20 back to being just regular past-tense. If it wasn't intentional, I would tighten up the grammar and switch it back to past tense.

Overall, a very enjoyable read. Not bad for a first (or second, or third-anything short of a final) draft.