Two possibilities occur to me. You could have a look at Plato's dialog "Apology". It tells the story of Socrates facing execution, and is one of the great pillars of Western civilization. It's a good introduction to Plato's style, and not too heavy.

And/or you could all the way back to the beginning, and look at the Pre-Socratics:
www.amazon.com/gp/product...724-3217529

This includes the main figures who did philosophy prior to Socrates and Plato. We have no complete works from any of them, so we have to conjecture what they must have meant by piecing together fragments they left behind.

I think this is a nice way to get a sense of the kinds of questions these guys were looking at, and you can bounce around between some of the main figures. You'll see stuff by Pythagoras, Parmenides, Zeno, Thales, Anaximander, and others too. Some Big Names.

Along with Plato and Socrates, the other colossus of Greek Philosophy is Aristotle. I don'have a recommendation for what to do with Aristotle. I find him a tough read, myself. I guess it depends on your interest - he wrote on many, many subjects.

A really wonderful book is Pierre Hadot's "What is Ancient Philosophy?". It is not an easy read - but at the same time it is incredibly well written (and well translated from the orginal French). Hadot is a "world-class" philosopher who was admired by Michel Foucault - and he has a very very very different approach to ancient philosophy from the soulless drivel that "analytical philosophy", which predominates/suffocates the philosophical mainstream in the English speaking world, churns out. The primary difference is that Hadot takes ancient philosophy seriously and attempts, to the extent that it is possible, to understand it on it's own terms. This is especially telling in Hadot's treatment of Plato and the tradition of Platonic philosophy in late antiquity (centuries after Plato). The book is somewhat controversial because Hadot makes no bones about his opinion that the rise of Christianity brought an abrupt end to the tradition of free inquiry and spiritual exploration that was ancient philosophy (although this is simply a well documented historical fact). Hadot optimistically chose to title the book "What IS Ancient Philosophy" (rather than "What WAS...") - and he makes it clear that he wishes to encourage people to resume the "practice" of philosophy as it was, and still can be done - and lived. This might make the book sound like some kind of new-agey "self-help" crap - but it is a serious and at times demanding book. However difficult it is it is well worth the effort to read! Here's a good review from the New York Times: query.nytimes.com/gst/fullpage.html .