It's an interesting start and I'm definitely curious to know what actually happened. It's a good lead in and a nice little mystery sentence at the end. You're mixing sparse dialogue with solid descriptions to paint a very simple but vivid scene. Nicely done.
There was a funny pronoun in the second paragraph ("you") and in the third paragraph I might move the injection after "surprised", but those are pretty minor preference points. Well done, I'm interested to see where it goes.