I recommend Fr. Anthony Cekada's recent book:
Work of Human Hands: A Theological Critique of the Mass of Paul VI
It's a detailed survey of the spread of modernist influence throughout the church in the 20th century following the papacy of Pope St. Pius X. Although most people date the implosion of the church from the '60's and Vatican Council II, by the fifties, things were already coming unglued. Several chapters are available for reading online.
Spot on.