Okay, now for the PLOT NUT (nope, that's not a fan who has all the plotlines in the old STAR TREK series memorized.) What I'm talking about is a "helper" for your plot bolt. It's a reaction to the plot bolt that strengthens the connection. It's the equal and opposite reaction to whatever it was that prompted the "plot bolt." And it starts an entire string of events by its very presence or existence. This is tough to explain without an example. So--
Let's take an example from my upcoming standalone traditional novel,
Twist the nut on a little: Kimmie shoves in a blank DVD where there's a convenient machine and records the whole "show." Then she mails it to, um, the local TV station--these two are high-profile city council members, let's say, and are assumed not to be involved with each other because of a conflict of interest, not to mention that they are both "taken." Whoa--the plot thickens! The station manager shoves the disc into his pocket and heads off to blackmail Chris.
On the way, the station manager has a fender-bender with a little old lady (in her car, not as a pedestrian!) as he's headed for the council meeting to confront Chris. He throws off his overcoat (which lands somewhere on the hood of his car) to change her tire and then to help the man hook up the tow truck for his Ferrari (these things are expensive, you know--you can't have Just Anyone touching the axle, or whatever.) The video DVD (you saw this coming, but you were giddy for it to happen, weren't you?) slides out of his pocket onto the pavement, of course. The tow truck guy picks it up to hold it for him and forgets to give it back. Guess what is in the pocket of the tow trucker's coat when the trucker gets back to pick up his wife, who runs the city's biggest day care place . . . and the owner's bratty kids pull it out, thinking it is their Rainbow Frog video he promised to get off the Internet for them. Suddenly, on the screens of the kids' day care room, there is a suggestive picture that does not go unnoticed. . . .
As someone said, imagine those smart missiles during the Gulf war suddenly showing DEBBIE DOES DJIBOUTI. And trying to find THAT target. (Not to worry: nothing graphic is going on at the beginning of the recording, at least not YET.) It's not a pretty sight, all those caregivers and mothers screaming and dashing for the DVD player. The one who ultimately snatches the disc out is the best friend of Chris's long-time girlfriend, a woman who has long hoped to "wake up" her friend and make her dump Chris because of what she feels are his Unethical Practices. She'd love to get him off the city's power base.
Now she has the ammo!
I'd say that this item is a little more than a maguffin, perhaps a Plot Nut that holds that Plot Bolt (which was the intersection between the Kimmie-is-stalking-Christopher thread and the City-Council-Scandal thread) firmly on. It helps to make the coincidences and implausibilities in the plot seem a lot less so.
I've used this technique to connect two wildly varying plotlines, such as subplot 1, the girlfriend who wants Chris and her friend to break up (hey--possibly so that SHE can snag Chris for herself, or so she can snag her girlfriend for her homely brother Gus who is in place to console her . . .) and subplot 2, the mayoral race in which Chris hopes to be a candidate, and which would be lost for him if he were caught fooling around with Diane, who is the wife of the current mayor. (This book is part screwball comedy.) Tensions heighten and the audience squirms in delicious anticipation of the blow-up that is sure to come.
Let's try something more subtle. Henry does not talk about his family, ever. In this mystery, the prologue and some scenes from the (unnamed) murderer's POV have established that he's doing it to protect a secret in his family. Every time anyone asks about Henry's holidays, relatives, etc., he quickly deflects the question, never having to answer. (There's the plot bolt.) Everyone suspects Henry, of course. (A nice diversion.)
Late in the book, Theo (our sleuth) is at a party where the punch is spiked and also (unknown to any of the party-goers) doped with a fashionable party drug. Theo (our heroine) is the only one besides Henry (and the real killer) who does *not* drink the Mickey Finn punch, leaving her the only one to deal with the killer who drugged the punch. Naturally, she's now convinced Henry didn't drink it because he spiked it, and therefore the killer blindsides her when he takes Henry hostage. The hero arrives, and the two of them play out the final confrontation with the killer, who now has Henry as a hostage. (Here comes the plot nut.) The reason Henry never spoke of his family is because he's ashamed: his father, who's all the family he has, has been jailed for (hot checks?) drunk driving (and has dodged the bullet once with a vehicular manslaughter charge) and is an alcoholic. And that's why he didn't drink the punch: he saw the gin being surreptitiously added, and he won't touch alcohol. The suspicion (a bolt throughout the book) is answered and ties right into why he's the only other one left on his feet for the confrontation, forming a plot nut.
Naturally, MOST of the best plot bolt and nut combinations are serendipity. Usually, when you were writing the first scene, you didn't realize why you were putting in that part about the alcoholic daddy until it came time that the later scene was flowing from your fingertips. And then people ask how you come up with these tight plots. Only another writer could understand the unexpected thrill of that plot nut screwing into place!
You can, of course, plan a connection between your subplots from the very beginning. That's why the subplots are there--to enrich the main story--and thus they need to be related. If you can come up with something that really sets up conflicts between major characters, such as his being a pilot and her being totally petrified of any thought of heights or flying, so much the better. Then she'll HAVE to get in the plane with him, barfbagging it or cowering on the floor of the light plane while they do the dogfight, or whatever. Conversely, maybe she turns out to be right about heights when he realizes the plane will NOT get off the ground in the shape that it's in, and then they jump out and let the criminals steal it and crash it into the stand of trees just across the road from the airstrip.
. . . this is called "setting up your crisis early" with things that your critique group tries to get you to cut, claiming you don't need these little hints that are obviously in there only for characterization. NOT!
The heck with them, say I. Plan your plot bolts, and place them throughout your book to strengthen it.
And if you find a nut for one of them, twist it down tight!