Basically, the human body has an in-built limit to how many times it can be forced to move across the timeline. It is a hard limit; it can't be known, and it most certainly can't be changed.
Its value is different in any given individual, and - although many have theorized - nobody knows whether it depends on genes, luck, physical health, spiritual inclination or pure happenstance.
It happens to every Time Agent sooner or later... even you.
The End of Time: it's where Time Agents – misfits of normal-flowing time – dwell and operate. From here, they travel through different eras to ensure no event is disrupted by any time traveler such as themselves.
You've been a Time Agent for a while, but it's the first time you've been to Café Bouvardie, a popular spot to relax for your kind. There, you meet the two owners of the place and listen to their stories...