This thoroughly documented study proves that there is a reasonable and positive doubt concerning the validity of the episcopal consecrations performed by Archbishop Pierre Martin Ngo Dinh Thuc. Bishop Kelly explains the teaching of the Catholic Church that sacraments of doubtful validity are invalid in the practical order.  Thus, the Catholic faithful must avoid receiving the sacraments from bishops and priests who derive their orders from Archbishop Thuc. Also in this book, Bishop Kelly refutes the calumnies of Father Donald Sanborn's April 1995 Letter to the Catholic people about Bishop Alfred Mendez, the retired bishop of Aricebo, Puerto Rico.