The term you're looking for is "gripping," not "holding on." As for exciting, if the story's any good, it should lend itself to high action and high intensity scenes. If it involves a bunch of people sitting around a table or coffee shop, either throw it out, turn it into a cable TV script, or make it a Jane Austen rip off. Otherwise, just keep throwing one attack after another at the hero. Keep him on the back foot and reeling until all the pieces fit together and he figures out what he needs to do to take down the bad guy and resolve the ending.