Here's The PikeCast going into The Eternal Enemy. My main takeaway from this episode is that I'm old. There's a generation who think $250 is insane for a VCR, but $900 for a phone is fine.
The book was published in 1993, the same year as Road To Nowhere, The Immortal and The Wicked Heart. It's scifi rather than horror or mystery, and from what I recall it had none of the real spiritual stuff found in many of Pike's novels. According to the PikeCast, the story makes nary a lick o' sense.