Ask HN: How should I present computer science to high school students?

I volunteered to help a friend (a physics teacher at a local high school) by presenting computer science to the science club he in charge of. I believe the idea is to give about a 30 minute presentation to expose them to the topic so they can decide if it's something they want to pursue further, perhaps in college.

The students range from sophomores to seniors in high school with at least some interest in science and mathematics. The presentation can get technical even it's a bit over there heads. Also, I just found out they can have access to laptops for each student if need be.

I'm looking for ideas on how to present the topic in an interactive and attention keeping way.