Frank Sheed mentions apokatastasis as a non-orthodox belief in his book, Theology and Sanity. What is it?
Apocatastasis (or apokatastasis) is defined in the Catholic Encyclopedia as “A name given in the history of theology to the doctrine which teaches that a time will come when all free creatures will share in the grace of salvation; in a special way, the devils and lost souls”. The doctrine was formally condemned at the Council of Constantinople in 543.
For more information see Apocatastasis.