Invasion - Dean Kootz

The story begins with a thirty-two-year-old Los Angeles police officer named Jack McGarvey. Jack is caught in a shootout at a gas station. He kills the gunman but is badly injured and spends months recovering in a hospital. When Jack returns home, the McGarveys receive a letter stating that Jack has inherited the Quartermass Ranch in Eagles Roost, Montana from his late partner's father, Eduardo Fernandez.