Infernal Devices, by K.W. Jeter, (c) 1987.
This is pretty much science fiction, since the entire plot hinges on the Victorianesque pseudo-science of 'aetheric vibrations of the brain' and on the existence of a sentient amphibious race of people.
There's really only one mad scientist in this book, and he's dead, even. That would be the protagonist's father, whose inventions are the 'infernal devices' of the title.
The entire grand mess was started by his seaweed-harvesting machine, which murdered an entire sentient race of beings, and it was finished by his son, who in his own way was an invention, a device, a tool.
George Dower, Sr., is "of that nature, that cares not for whatever consequences may ensue from its genius." This is not just science; it is uncaring science, one divorced entirely from any considerations of morality, and the results are very nearly cataclysmic.
George Dower, Sr., may have been a genius, but he was one who left naught but chaos in his wake, with his, as the title says, infernal devices.