By its very definition, a summary does not go in-depth; if it did, it would not be a summary.  A summary should touch on the most important points of a work and give the potential reader an idea what to expect, but in no way should it be construed as a substitute for reading the actual work.  There are plenty of summaries of Plato's Republic out there, but I guarantee you, not one of them could begin to approximate the themes and shades of meaning inherent in that work.  It would take pages and pages of writing to adequately explore everything Plato accomplished and no summary would ever begin to touch it.   

Since Plato's Republic is a long and complex book, it's important to read the entire book rather than rely on summaries. Most scholarly books on the Reupblic are longer than Plato's text.