The first half of the book is pre-revolutionary history, so a bit less controversial; House rather charmingly tries to draw parallels between Russian and English church history (it's pretty clear that his audience is the liberal English churchgoer), such as the fact that Henry VIII and his contemporary Ivan the Terrible were married several times and reformed the church. Er, yes.
The second half of the book reflects House's own experiences in outreach from the Anglican community and the World Council of Churches (for whom he worked) to the Soviet Union. He has to be a little guarded in what he says about those still living - who could know for sure what the outcome of перестройка would be? - but he is quite clear about the extent to which the Church was alternatively oppressed by and then forced into collusion with the Communist system.
It's not a complete account, as House admits in the foreword; the Armenian, Georgian, Baltic, Jewish, Muslim and Buddhist stories of religion in the USSR would all be a bit different (not to mention the complexities of Belarus, Ukraine and Moldova). And like most of us he has no inkling of the revival of the Orthodox church in the 1990s, and its unsavoury links with nationalism and closeness to the new regime. But you can't expect that from 130 pages written in 1988.