Like anything by Ian McEwan, it's beautifuly written. 
That said... 

Joe deleted 30 voicemails left by this stranger, then pouted when no one took his accusation of harrassment as gospel. As a man with a science background, why would he delete the voicemails? No one will simply have faith you're being harassed. Evidence is required with these acusations. Dr. Surprised Pikachu was annoyed for way too many pages.

In so far as his relationship with his girlfriend-- it teetered on "idiot plot." He went out of his way to be secretive, hateful, and weird about his concerns with Perry. The police may not have been in his corner, but she could have been if he had clued her in more and had some patience.

Overall, it was well written and suspenseful, but geeze, it left me wanting in way of plot. In way of... common sense? In the end, I didn't care for any of the characters. I just wanted resolve. I guess I got that much, but it was unsatisfying.