The Case of the Toxic Spell Dump by Harry Turtledove
It's been a long time since I read any of Turtledove's work and this one (along with a few others) has been sitting in my reading pile for years. A reorganisation of the large pile into several neat stacks (thereby allowing me to enjoy the illusion of progress) happened to bring this book to the top of one stack, so I finally picked it up in the hope of enjoying some light entertainment. I was not disappointed….
Source: Cool Sci-Fi