It's not the book you want; it's the book you need.
I recently picked up this book for a second read. I first read it 7 years ago and, like the other reviewer, I was disappointed about the lack of detail about ghosts, demons and so forth. No, Peter Bolt doesn't tell you everything you want to know. No, you don't find out how houses get haunted or whether mediums really contact the dead.
What you get is an engaging exposition of what the Bible says about the spiritual underworld and what the gospel has to do with it. Bolt does his job as a good preacher ought to: sticking to what the Bible says, giving biblical weight to each subtopic, communicating in a way anyone can understand, making Jesus the point of the whole thing. He doesn't try to satisfy our curiosities, just as the Bible doesn't. He does connect his subject matter with Jesus Christ, just as the bible does. If you want a brief statement of the book's core message, read Hebrews 2:14-15.
I appreciated the book's structure, starting at the Bible's margins and moving to the centre of its message. I also appreciated the analogy to the criminal underworld. It furnishes many helpful illustrations.
I recommend it for both unbelievers and believers. Readers should go in understanding what kind of book this is and what it seeks to do, to avoid disappointment. I appreciated it more on my second read, as a more mature believer. That's because I understand better my great need of being pointed to the Lord Jesus Christ.