"William E. Emba"
This Lord Peter Wimsey novel is often considered Sayers' best. The plot revolves around the art of change ringing, often called "campanology" by non-campanologists. As usual with Sayers, she makes no explanatory concessions to her less-than-completely-educated readers (in this case, mostly Americans), so see http://www.changeringers.karoo.net/ [BROKEN LINK -- See note below from Peter Adams] for general
information about change ringing, including a glossary.
Change ringing has an inherent mathematical content. Because of physical
limitations and safety precautions, one can only move up or down one bell
when ringing, and the art is thus focussed on generating permutations from
these interchanges. (Playing tunes is simply not done.)
Sayers refers several times to this mathematical content, including having
one character who has written a book on the mathematics of change ringing,
and an encryption algorithm based on change ringing permutations.
In addition, most mathematically-minded readers will identity the killer
long before Lord Peter figures things out, just by metafictional reasoning.
This is deliberate with Sayers, who often scorned the traditional whodunit
thrills in favor of writing for the sake of writing.
American readers should know that the title comes from an English saying
"Nine tailors make a man". Its meaning and origin is unknown, but it is
usually explained as being based on the traditional nine bells, that is,
the nine tollers, rung at a man's death.