Display specific post only

I have a category heading on the left with all posts in that category listed below. When the user clicks on a specific post, I want that post (and that post only) to display.

I used I used query_posts($query_string.'&posts_per_page=1'); but when you click on a specific post in that category, only the most recent post shows up.

How can I just display the selected post, and that post only?

Thanks!!