The Golden Bough opens with a puzzle rather than a thesis. At Nemi, in the Alban hills south of Rome, the priest of Diana held his office by having killed his predecessor, and held it until someone killed him. He was called the king of the wood, and a challenger had first to break a bough from a particular tree. Frazer asks why, and takes twelve volumes to answer.
The answer assembles a theory out of thousands of reported customs. Kings are identified with the fertility of the land and are killed before their vigour fails, so that the power passes on undiminished. Behind that stands the dying and reviving god, Osiris, Adonis, Attis, Tammuz, whose death and return are the seasons. Behind that stands magic, which Frazer divides into the homeopathic, where like affects like, and the contagious, where things once in contact remain connected. And over the whole he lays a sequence: humanity works by magic, finds it fails, turns to religion, finds that fails too, and arrives at science.
The first edition of 1890 was two volumes. The third, published between 1906 and 1915, was twelve, with a supplementary volume in 1936. The one-volume abridgement of 1922 is what most people have actually read, and it leaves out most of the qualifications.