The novel Presumed Dead is a crime fiction story in which a forensic scientist, Dr Phillip Keane painstakingly reconstructs the disappearance of feisty Councillor Jane Kenwood. He and his think tank attempt to associate each of 4 types of evidence, as either cause or effect, with other evidence in a causal hypothesis, one of 8 linking from the final victim’s condition back to the earliest perpetrator’s motive. This is shown in the diagram, in which each arrow is a causal hypothesis from cause to effect, going from step 8 to step 1. Of course, the evidence won’t be discovered exactly as in this sequence, but by investigating the possibilities in this sequence their approach is methodical, efficient and comprehensive. The efficiency is achieved by conceiving of it as a ‘Euler walk’, a logical pathway connecting nodes without repeating links, a foundation of graph theory in mathematics. With this strategy, the friends investigate the abduction, piece together events and search for missing evidence. It is a strategy that could probably be used for other crimes of motive and victim e.g. murder, assault, arson, theft, fraud and property damage. The novel also illustrates ills of partisanship in town hall politics and how they are conquered by an iconic independent woman politician. Reviews are on my blog: martinknox.com