The plan

He leads the team's repair missions into the past and learns how little the Chrono-Censor lets them change. Then he meets an older version of himself who has mastered time and wants it undone, and has to stop his own future self from collapsing the timeline. Underneath it is the fear of becoming that man. The final fight happens inside the black-hole core, the one place where a time traveler can really die.

The constant flow of visions overwhelms her, and time travel may amplify or destabilize them further. What she wants is peace, a life without the burden. She gets it at a price: when the team is tethered back to the present and the cosmic balance realigns, she loses her powers.

As she works with the team, her neural circuits evolve and she begins to feel things she doesn't understand. She wants to know what being human means and where she fits in the timeline. In the final jump she's critically damaged, and the rewiring leaves her more human than before.

He wants to prove that even with his cybernetics he is still a man capable of emotion and loyalty. He proves it in the final jump, when he sacrifices himself for the team.

He became "Post-Tethered" and then "Free-Tethered", able to tether himself at will and slip past the Chrono-Censor. Having seen what time travel does, he's determined to erase it from existence, even if that means killing his younger self, which he can only do inside the black hole, where the Censor doesn't reach. In the end he destroys the fusion core inside the black hole and seals time travel forever. The early notes gave him the codename Deus Ex Machina, for the way he drives the story from outside it.

The government seizes his machine almost at once and builds the Epoch Project around it. In the early brainstorm the older Duo's endgame reaches back to him and his machine directly.

The earliest brainstorm put the program at Area 51 in Nevada instead; the bible settles on the Voltaire.

The Chrono-Censor doesn't exist inside it, which makes it the one place a time traveler can truly be killed, and the place the final battle is set. Destroying the core ends time travel forever, and in the story's Cosmic Reset, nuclear energy and black holes stop existing with it.

It keeps the missions small and forces the team to find subtle ways to change things. The older Duo has learned to bypass it, and it has no power inside the black hole.

Finding out who is opening them, and why, drives the team toward the discovery that they are not the only ones jumping through time.

When it finally works, the side effects are severe: Ethan dies, Chance is rewired into something more human, and Gwen loses her powers. The older Duo has gone past it to "Free-Tethering", tethering at will.

The fire turns out to have been set on purpose, to hide something, and it's the first sign that the timeline has been tampered with by someone other than them.

Its first team is Duo, Gwen, Chance and Ethan, the first four able to jump. Its job is repair work on a fragile timeline, and its missions keep revealing costs nobody planned for.