The Documents in the Case
Dorothy L. Sayers co-authored this novel with Robert Eustace (who primarily presented her with the scientific foundation for the crime). It is an experimental work, presenting the evidence for the case in the form of letters, newspaper clippings and statements.
This procedure means that it is never clear what is true and what is false; none of the narrators is trustworthy, and one of them is even represented by others as going mad.
It is never clear either where one's sympathy should lie, not until very late in the book, and even then there is an equivocality that makes reading The Documents in the Case in some respects a scary undertaking, because ones choice while reading is so telling of ones one personality.
All in all — and to keep it short — this is one of the most interesting Sayers' novels, precisely because it is experimental. Also, the theological discussions that sometimes erupt are interesting in themselves.