I've never read much Dean Koontz and my impression of his later and longer work (see here) has not been very good, but Shattered proved out to be short, gripping and brisk. It's one of Koontz's early books, published initially under his K. W. Dwyer pseudonym (and later on published as Dean Koontz), and still it tells a full-bloodied tale of full-bloodied people.
The premise is not very different from Richard Matheson's and Steven Spielberg's Duel which is two years senior, so Koontz may have had it in mind. Shattered also differs from Matheson's work in that the chase is personal in tone. A dark, mysterious van is behind two drivers, a young boy and the boyfriend of his older sister, who's a father figure to the kid. They don't know who drives the van, but Koontz shows he's a menace in the chapters narrated through the mysterious driver.
The ending is a bit too abrupt and there are some characters of which I didn't know whether they really were necessary. But Shattered is still a
suspenseful book that feels for its doomed characters.
This came out in Finnish in 1994 from Book Studio under the title Varjostaja. See the Finnish cover here.
More Forgotten Books here.