So the thing here is just before certain people die they are... replaced by... people from the future. These Travelers take over the body- and the life- of the person who just kicked it. We first meet Marcy, who's intellectually impaired and under care of a social worker named David, who's a little surprised to discover she can suddenly read just fine. They have an interesting relationship, and we'll see as time goes on how in some ways they're the heart of the show. There's also Carly the tactician- also a single mom, Trevor the techie (high school) and Phil the team's historical expert (and a junkie). Oh, and Mac too. Played by Eric McCormack (of Will and Grace)- the team leader and an FBI agent.
The first episode shows us what these peoples' lives are like (or more accurately, the mess some of these Travelers inherit)- while also raising the question: is it morally acceptable to take over someone's life and not tell their host's significant other? Probably not. At any rate David and Marcy are cute- but we're going to get into all the is it appropriate for them to have a relationship stuff? He's trying to figure out how she went from intellectually disabled to sharp as a whip literally overnight- and Phil uses his knowledge of the future to get himself out of a scrape with the law.
The team has to get Mac into place so he can be replaced by his counterpart from the future. And poor David. He gets kissed by Marcy and has NO idea what's going on. Meanwhile, Carly's abusive ex is also a cop, which will cause issues. There's a powerful moment when Phil witnesses the heart attack of the cop after him, and can't intervene. Anyway... we get to the point where our agent Mac meets the rest of the team. And- voila- the team is assembled.