In the early days of film-making, a popular technique for bringing audiences back to the theater was to leave a protagonist hanging on for dear life at the edge of a sheer, rocky cliff. Will Ranger Bob survive? Come back next week for Episode 2 in a three part series!
Cliffhangers are as interesting and useful today as they were a hundred or more years ago. The fear of death is universal. Leave your protagonist in mortal peril and most readers will be reluctant to put your book down. At least not until they've read the next chapter to make sure the hero survives. (Or cheated and skipped ahead!)
Some of the most annoying (i.e. best) writers find ways to drag the cliffhanger out. A cliffhanger can be especially effective in a novel written in multiple points of view. Being a linear type of reader, it hooks me almost every time when an author ends one character's chapter with a life or death situation then starts the next chapter in a different character's point of view. I'm either forced to wait twenty pages to find out if Character A survives or (Yes, I'm guilty of this!) skim through chapters until I find the continuing thread of Character A's story. Either way I spend more time reading than I intended.
If something sounds oddly familiar about this technique, that's because a cliffhanger is nothing more than an unanswered question involving higher stakes. Cliffhangers inspire the same kind of morbid curiosity that makes "rubber-necking" motorists slow down to gawk at an accident on the opposite side of the freeway. Even though we assume an author wouldn't kill off the main character in the middle of the story, there's still a part of us that needs to know everything will turn out all right.
So leave that gladiator in the bloodied sand with a sword pointing at his neck while you send your reader on a detour to the senator's opulent villa at the outskirts of Rome. Maybe Ms. Reader will get annoyed and skip ahead, but she's still eagerly reading your story, and that's what you're shooting for.
Will we make it through the next three techniques? Will it be worth the wait? Tune in next week for Episode 3: Raising the Stakes.