Show Excerpt for non registered users

Hi,
I've created a user category called Stranger and then a Free User. The stranger is set for the people not logged in to the site. I've blocked the category Filmer for Strangers. What I want is for them to se the Featured Image and Excerpt for the posts in Filmer on the category page. But when they click a post they should not be able to see the full post but instead have to register. How do I do this?

Thanks