This is an amusing story, less fantastical than the Ripping Yarns series but still tending towards the absurd. It tells the story of an Anglican missionary returned from Africa who is asked by the Bishop of London (a fictitious character rather than the real one of the era) to establish a Mission for Fallen Women in the London Dockland on behalf the Church Mission Society (one wonders what the real CMS thought of this). The missionary succeeds - but only because he meets the sexual needs of a benefactress and of the girls he is sent to help. This is not, though, a vulgar "sex comedy" of the Confessions of a Window Cleaner type, and although the theme is distasteful when considered in the abstract (I expect it would be more controversial today), Palin's congeniality prevents the reader (or viewer of the film) from dwelling on that very much.
The book has a few "value-added" points that are not in the film, such as a short introduction. The film has been criticised as being somewhat "murky", and the low resolution colour photos throughout the book (captured from video, it looks like) don't do much to enhance the volume.
A scene in which the hero's financée understands "Fallen Women" to mean women who have broken their leg was famously criticised by two student interviewers as unfunny, leading to the only recorded instance of Palin expressing real anger - Palin apparently ended the interview and stormed out of his own house close to sobs.