Here's a quick synopsis, lifted from Amazon.com/Publisher's Weekly:
Christopher Priest's novel (the title of which refers to the residue left after a magician's successful trick) is enthrallingly odd. In a carefully calculated period style that is remarkably akin to that of the late Robertson Davies, Priest writes of a pair of rival magicians in turn-of-the-century London. Each has a winning trick the other craves, but so arcane is the nature of these tricks, so incredibly difficult are they to perform, that they take on a peculiar life of their own?in one case involving a mysterious apparent double identity, in the other a reliance on the ferocious powers unleashed in the early experimental years of electricity. The rivalry of the two men is such that in the end, though both are ashamed of the strength of their feelings of spite and envy, it consumes them both, and affects their respective families for generations. This is a complex tale that must have been extremely difficult to tell in exactly the right sequence, while still maintaining a series of shocks to the very end. Priest has brought it off with great imagination and skill. It's only fair to say, though, that the book's very considerable narrative grip is its principal virtue. The characters and incidents have a decidedly Gothic cast, and only the restraint that marks the story's telling keeps it on the rails.