If you head over to Tor Books' website, you'll find a lot of essays on Pike's work, and I'll be posting links to all of them, but here's the latest, from Alissa Burger.
[In Pike's books] characters regularly find themselves contending with the lingering evils of the past, visitors from the future (both malevolent and well-meaning), the depths of the cosmos, and complex spirituality. Three of Pike’s novels that tackle some of these thorny issues are See You Later (1990), Whisper of Death (1991), and The Wicked Heart (1993), though there are several others addressed in previous columns that are part of this larger discussion as well, including Chain Letter 2: The Ancient Evil (1992), Road to Nowhere (1993), The Eternal Enemy (1993), The Immortal (1993), and the Last Vampire series (1994-2013).
In Pike’s universe, the past is never really past, with echoes of evil that carry down through the years, influencing and shaping the events of the present. (Source)