Let’s be honest from the start. We’ve all read a book or seen a film where the hero / heroine or another main character suddenly develops a previously untold skill. In other cases the killer has turned out to be a character so peripheral to the main plot that logic has flown out of the window along with your interest.
For me nothing kills a story quicker than a new skill / villain first appearing five pages from the end of a novel. This is clearly an author not knowing how to finish the story and deciding to invent a skill or character just to finish off the story.
Foreshadowing is the term for drip feeding information throughout the story so that when the conclusion happens, the plot is plausible and the reader is left feeling satisfied rather than cheated.
It can be something as simple as having a character washing their judo clothes or meeting someone from their judo class for a drink. This tells the reader that the character knows some martial arts, so that when they start kicking butt it’s natural action.
Again introducing a peripheral character throughout the novel works, provided you give the reader enough information to remember the character. Cycling past on page seven of a three hundred page novel isn’t good enough and anyone doing this deserves all the scorn they get.
One of the best pieces of foreshadowing I can bring to mind is the film Die Hard. The hero is tense on a flight and a fellow passenger advises him to take his shoes and socks of when he gets to his hotel and make fists with his feet. The hero duly does this and later in the film when he is still barefoot he is hiding in a room with glass walls, the head baddie who had already seen the hero was barefoot told his men to shoot the glass. The action then cuts to a scene where the hero is standing on his bare tip toes with broken glass all over the floor.
As usual comments and feedback are always welcome.