Watchers: Dean Koontz

At the beginning of the book, a psychotic killer is paid to hit 4 doctors. They all worked at the same lab. A man, Travis, is out hiking to try to find meaning in his life and runs across a dog and some mysterious being in the woods. He and the dog run all the way to his car, and he takes the dog home after he realizes the dog can understand what he is saying. We find out 2 creatures escaped from the lab. One is a dog, who was created to be as smart as a human, the other is a baboon hybrid, created to be a killer. The baboon creature spends months stalking the dog, who with Travis, travels a few times. In the end, Travis ends up killing both the baboon and the psychotic killer, though we never really get confirmation that the killer is dead. The dog goes on to have puppies that are as smart as him.