OK, basic premise: Fantasy world in which two distinct styles of magic exist - shadow magic and light magic. Shadow magic was invented first, and used to be the predominant kind of magic, but when light magic was discovered it rapidly overtook shadow magic in popularity because it has fewer side effects - if you use too much shadow magic, it'll drive you insane. Shadow madness has two distinct stages: in stage 1, you become a psychopathic serial killer; and in stage 2 you lose touch with reality and start having hallucinations and delusions. Stage 1 guys are more dangerous because they can fake normal and because in stage 2 it becomes hard to concentrate enough to cast spells. However, light magic has a drawback too - there are some beings that are immune to it. Light magic acts on the person's soul and affects their body only as a byproduct of affecting their soul, so beings without souls are unaffected by light magic. (Shadow madness, incidentally, is due to a damaged soul, and therefore shadow mad people are resistant but not entirely immune to light magic.) As a result, a small number of people keep the practice of shadow magic alive, being careful not to overuse it, just in case a threat arises that light mages can't handle. Five years before the story starts, a rift opens between dimensions and soulless beings from another dimension pour into the world, causing mayhem and destruction. All available shadow mages rally to fight them, and eventually succeed in beating them back and closing the rift. Unfortunately, many of the most experienced shadow mages go insane during the rift war, and most of the rest of them are bordering on going nuts themselves. So some guys get together a task force of several of the most skilled apprentice shadow mages, because they're inexperienced enough not to be in much danger of shadow madness yet, but they're skilled enough to actually stand a chance if they're clever. The team consists of five shadow mages plus a light mage who's assigned to keep an eye on them. They go around to places with a series of suspicious deaths, and at each place they investigate the local shadow mages to see if any of them have gone into stage 1. If they have, the team tries to capture or kill them. They soon discover that several shadow mages (mostly on the border between stage 1 and 2) are planning to try to blot out the sun in the belief that this will make light magic impossible and shadow magic more powerful. In reality, it'll just kill everyone - all the crops will die and the world will get too cold and so forth. They're also going to discover that one of their team is a mole, who has been in stage 1 since the start of the story; his mask starts to slip as he enters stage 2. My big problem is pacing. Right now, I'm getting bogged down in their first capture. I'm not sure how much detail to go into - I'd kind of like to skip past it, but it feels wrong not to explain how they investigate and catch the guy. I'm also worrying about how to balance hinting at the mole being stage 1 while still making it convincing that no one figures it out too soon. (Plus ensuring my readers don't figure it out too quickly.)
I feel like you should start it off with some action, and explain the back story through dialogue. You should also hint as little as possible towards the mole.
Ninety-nine percent of the time, the best way to convey important backstory information is by slipping it in naturally. For example, "His teeth chattered as he dodged the sidewalk crowds, splashing up mud and wishing he'd brought an umbrella" lets readers know that it's cold, raining and in a crowded place without creating some long paragraph about what the setting looks like. Do the same thing for this: make little comparisons, brief references, etc. but slip them into sentences rather than writing sentences/paragraphs that exist solely to expand on the backstory. Also, keep in mind that a little bit goes a long way. It only takes a few well-placed snippets to give the info needed (most of the time). If it's something that really needs a flashback or an excerpt from the past, do it, but make the flashback feel as vivid as a real-time scene -- and avoid cliche phrases like "His mind began to wander as he drifted back into memories of the past." That tends to annoy people. I agree with this. Hope I helped.
I've found that if I have a difficult time incorporating a hint into a scene that it's actually easier to write the rest of the scene and to come back to it later. Sometimes being able to just get out the scene out of my head, then going back to it later actually helps me to figure out how to incorporate it or whether I need to add more detail. I think the most important thing is to not get hung up on details when you're writing your draft, add it in later if you feel it will drive the story more effectively.
I'm of the mind that you should write the first draft as if the reader already knows the backstory. I think it is easier to slip in the bits of information the reader actually needs after the fact then it is to try and remove all the extra crap because you told all the backstory.
