Courier

Meet Bob, your local courier.
You've barely noticed him. You've barely even looked his way.
But he's noticed you. He's noticed everything about you.
He's been paying very close attention indeed.
And he likes what he sees...

You by Caroline Kepnes meets Engleby by Sebastian Faulks in Courier, a gritty psychological thriller novella about loneliness, warped thinking, and the dark side of desire.