I posted previously about Greg Welty’s excellent book Why Is There Evil In The World (And So Much Of It)? when it was published a couple of years ago. In my (admittedly biased) opinion, it’s the best lay-level treatment of the problem of evil available today. I recommend it every chance I get.
If you want a taster, you can get it from this short article on the problem of evil, written by Greg for TGC’s Concise Theology series. It’s basically a much-distilled version of the argument Greg lays out in the book. If you like the article, you’ll appreciate the book even more!