It's 24XX AD and time travel has become a regulated service in future society. For the general populace, several forms of spectator-type time travels are made available to them for recreational and investigative purposes but only into the past and they can do nothing to affect it. For those in the know however, there is a more dangerous branch of time travel where they can potentially alter their reality as they know it.
One group of elite agents have access to one of these more dangerous methods and their duty is to correct abberations in the timeline. Unofficially however, they are also tasked with making sure that the one world order stays intact in the past. The slightest change can cause it to go off course so they need to force the "official" timeline no matter what the cost. Their missions center around the life of the Saint, the original leader of their utopia. He was a tortured individual later in life who grew through tremendous adversity and became the central figure of their future. To ensure history stays on course, they must facilitate the tragedies in his life as per his meticulously kept journal.
The story will follow a young woman fresh to their organization through their trips into the past for the first half to flesh out their world and the dillemmae their path brings them. The introduction of a mysterious sinisterly armored individual with far superior technology they designate as the Devil marks the beginning of the second half where the agency combats his quest to make their efforts in vain.
Their organization finds itself on the road to destruction as he chips away at them bit by bit as his interventions reveals that the journal they've been following contradicts what they've been led to believe about their cause and time travel itself. With their forces dwindling down to nothing, these agents chase after the Devil and truths behind the mysteries he brings.