The book contents apparently break down like this: Letter to Henry Miller.--Letter to Michael Fraenkel.--I. The Body.--II. The Death.--III. The Image.--IV. The Will.
In Bastard Death, Fraenkel elaborates on his ideas of "spiritual/soul death." As I have never read this book (though I'd love to), I can't really exlaborate on it much further. In a correspondence between Lawrence Durrell and Michael Hargraves in 1979, Durrell offered this observation about Bastard Death:
"I am not fully in the know concerning Fraenkel because I never met him; I missed him by a few weeks when I arrived in Paris. Miller was keen on his BASTARD DEATH at the time; me not very. It smelt of pretence and was wordy and windy...He seems to have been an endearing man and [Henry and Alfred Perles] would tease him to death and play upon his quirks like his meaness over money."
On April 23, 1936, George Orwell reviewed Bastard Death in New English Weekly (ref.). Unfortunately, I don't know what he made of it.
Fraenkel was finishing Bastard Death in 1935, when he, Miller, and Perles formulated the idea of creating a book of correspondence around the deathly ideas in his book. This became Hamlet. Disclosure: I don't own the Hamlet correspondence and have never read it! (it is top of my wish list). My impression, however, is that Bastard Death is explicitly discussed at the beginning of the book, but is eventually left behind for other subjects. Also, it's my impression that Miller's introduction to Bastard Death is re-printed in Hamlet. Maybe someone can correct me on this?
An internet search turns up used copies of Bastard Death going for as cheap as $20-30 (2nd edition), or first editions for around $80.