This theory states that the Church fell off the tracks and rolled down the hill as soon as it shot out of the first century. It was not restored until Joseph Smith came along in the 1800’s.
This is also held in some degree by the Seventh Day Adventists, the Baptists and other sects. Is there validity to this claim?
There is an excellent article on this topic written by Joe Heschmeyer, S.P. entitled Total Apostasy: the Big Issue Dividing Mormons & Catholics.