The book is Lightning and it is about Time Travel, also I hate it.  Since it came out in the 90's I don't feel bad spoiling it, thus;  In this book the characters can only travel forward in time, but then are allowed to be sucked back to their past, like Time Cop backwards but way super worse.  The theory they work on is that the past cannot be changed but the future can; although I have a problem with this already I am going to let the book keep being stupid.  It then goes on to say that the Nazis are trying to steal technology from the 80's to win the second world war for Hitler (again, going to let the choice of the 80's and not Futurama time slide for now).  Also people travel forward in time, then back to their past, I know I have already said that in this paragraph but it is so stupid it needs to be said again.

Three strikes, need to bitch like the little girl I am:

First off I should point out that instead of just jumping forward to the 80s when they could find things like the nuclear bomb info mildly easily, why didn't they keep going forward and find laser guns?  I would and I am not an evil Nazi, baby killing mastermind.  Secondly, if you can't change the past that means that jumping to the future, then back, makes that future your past, meaning you can't change that.  So when the book continues to change the future/past, but only in a way that allows the plot to move forward while hoping most readers aren't smart enough to get what was going on.  They are, this was just stupidly bad writing; like Garfield or Time Cop.

So here are three things that manage to get time travel correct.  Why?  Because it isn't hard to steal this concept that is already in modern fiction.  Also I wanted to make an attempt to tell the world about Primer, if even briefly.

Theory 1:

The black line is time and the colored lines are time travel jumps.  Basically fate, if you traveled through time it was because you already traveled through time before and you should be here, or there now.  This is probably the easiest to get right and probably the one that most people constantly get wrong.  Why?  Because most people don't keep notes about where things are going down and when, they should also draw diagrams and make models.   Maybe not the model part, but I am just a geek.    

As seen in: Primer did an amazing job, and sadly kind of describes what people think that time travel might really be like, in the entire "can't go past where you start" thing.  Time Crimes also managed to do an amazing job at keeping the timeline straight, although the story itself kind of managed to suffer along the way because after you figure out what is happening then you have kind of figured out exactly what happens next.

What Time Cop did wrong:  Changing the past was totally cool as long as someone didn't catch you doing it.  The entire effort was made to "maintain the time stream" even though no one really knew what the hell that meant.  There didn’t ever seem to be any cool crimes for them to stop anyway, just annoying money making ones.  Also why would killing one person (main bad guy from Heat Vision and Jack) make all of the future a brighter and happier place?  That just sounds terrible.

Theory 2:

Again, the black line is time and the colored lines are the jumps taken.  This basically says that regardless of what you do, you have never jumped to the past before, and by simply jumping to the past you have changed the future from what it really is.  While most of the stories out there don't really go out of their way to try and explain away what happens to the future that the traveler is from, or if they are jumping to the past or just creating an alternate dimension where they did go to the past.  Who knows, error free and kind of fun to watch people do what they want in a nearly consequence free environment; like the '60s but drugs are replaced with violence and lasers, same amount of hi-jinks though. 

As seen in:  Mainly the only place that does this right is the first two Terminator movies.  While all of the other ones, besides the Sarah Connor Chronicles that actively vomits on the rest of the story by allowing them to go forward in time (and allowing other travelers to pal around in the past), do manage to have this work as well by the virtue of it pretty much saying "we can still do whatever we want" they were bad movies and we should spit on the people who made them happen.

What Time Cop did wrong:  Why can't matter occupy the same place?  Also one person wouldn't be the same matter years in the future as he is at that very moment.  Nothing would be.  Things erode and change and even the electrons from that same matter would be in different places.  Even though the entire movie revolves around this concept, it is stupid and seemingly based out of special effects for when it did happen. Why didn't he just shoot the past one and use the same special effect on the future one.  That could have been cooler.

Theory 3:

This is what happens when Dr Who travels through time.  While this shouldn't really work, and while this pretty much goes against everything else that I have said here I choose to believe that he makes the entire experience work through sheer acts of being British/awesome.  

As seen in: Dr Who only.  He openly admits that his actions are pretty much causing a paradox, and that is why his machine works to prevent them and not allow them in the first place.  Take note though, this only works for Dr. Who. Also that it sounds stupid when you write it down.

What Time Cop did wrong: He wasn't British, just foreign.

Go watch Primer