Welcome (back) to the Mises forum!
Be sure to check out The Ultimate Beginner meta-thread (and the welcome thread there). It’s filled with helpful links with forum tips and how to’s as well as things you might want to look into in the future and refer back to.
As for your request, I’ll repeat what I mentioned here:
z1235 has been plugging the hell out of Beyond Democracy. Says he’s gotten a lot of positive results by recommending it. $0.99 on Kindle (or even borrow it for free if you have a Prime account.)
Other recommendations for good short ones would be The Law and Anatomy of the State. For more recommendations, I’d check out the One Book for Capitalism thread…but it seems like BD is going to be the ticket. It’s short and (evidently from z’s experience) is quite effective in bringing people around.
Let us know how it goes!