So you're interested in trying out Highsmith? My first suggestion would be "The Talented Mr. Ripley" but after finishing "A Dog's Ransom" it runs a close 2nd for a Highsmith recommendation. The story opens with a man receiving threatening letters from a stranger. From there the story introduces the themes familiar to Highsmith readers. There's the creepy factor of "this could happen to me". There's the vulnerability of the city and exposure to other people. The absence of children or their violent disappearance. Confusion over the seriousness of a relationship. Self examination and wondering about life. But I don't want to give too much away! It's a solid introduction to Highsmith and her craft.
The ending reminded me of "Miss Lonelyhearts".
I was reading some biographical material on Highsmith. I knew she had a terrible relationship with her mother. I had not noticed that children do not appear in her stories, or if they do they have generally met with a bad end. In this one it's gut wrenching to watch Ed Reynolds grieve the loss of his dog so soon after the loss of his daughter.