I'm currently reading "Lord Foulgrin's Letters." It is book one in a series and I read book two first - oops. The second book is "The Ishbane Conspiracy." I highly recommend them both. They are very similar to C.S. Lewis's "Screwtape Letters." They are set in our times with situations that adults and young people are apt to encounter. The best thing about both books is they open our spiritual eyes to the unseen battle raging and encourage us to equip ourselves for that battle.
We must put on...The Armor of God
"Finally, be strong in the Lord and in His mighty power. Put on the full armor of God so that you can take your stand against the devil's schemes. For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms. Therefore put on the full armor of God, so that when the day of evil comes, you may be able to stand your ground, and after you have done everything, to stand." Ephesians 6: 10-13