Neptune King and The Arsonist is the 26th book in the series. Neptune and Shark are as brilliant as always but is this the case that will ruin their hundred per cent success rate? Neptune begins to fear that when they're hired by Mrs O'Shea to catch the person who killed her husband by setting fire to their house. In the course of the investigation they solve three other crimes and let the police take the credit. First they solve the murder of Mrs Humbolt who was attacked in her home and then her house set alight, then Shark comes across a possible suspect for their case only to prove that he was responsible for a house fire in which a whole family perished. They're down to one suspect and to Neptune's dismay he proves that this man is guilty of vandalism not arson. Meantime their arsonist is escalating. What started with simple nuisance fires and hedge fires graduated to a house fire with an incidental death, to the burning of a warehouses and the destruction of a priceless ancient Chinese Emperor's shoulder carriage. When the arsonist steals a flame thrower and begins burning and torturing animals, Neptune is afraid he will escalate and move onto human targets. The stakes are high. This is one time both he and Shark come close to failure, at a time when it is imperative that they succeed.