This Is Us' Season 4 finale threw a lot of information at viewers in the short span of 44 minutes. Fans got to see Kevin and Randall's big breakup. There was a surprise twist for Kate and Toby, who decided that Baby Jack needed a sibling and started looking into adoption. Viewers also learned who the mother of Kevin's children (yes multiple children) will be, and that this may even be a marriage for the ages. But there were also some new faces introduced. Fans found themselves asking, who is Sadie on This Is Us? Warning: Spoilers for This Is Us follow.
The Season 4 premiere of This Is Us was entitled "Strangers," and it focused on three new faces: Cassidy, Malik, and the adult version of Baby Jack. All three of these characters are now no longer strangers, but part of the larger narrative, as was demonstrated by their appearances in the Season 4 finale.
But this finale was a bookend to the premiere, as evidenced by the title "Strangers, Part 2." In this episode, fans met three more new faces.
- The first, Dr. Eli Mason, is a doctor whose hobby is horses. He turns out to be Madison's OB-GYN, and he will help Kevin and Madison as they adjust to their new situation.
- The second is Hailey, who turns out to be living in 2050. She's the grown-up version of Jack's sister Kate and Toby will seemingly adopt come next season.
- The third is Sadie. She's Dr. Mason's daughter and a whiz at horses. But what is her connection to the story, other than her father?
When asked about these characters, showrunner Dan Fogelman wouldn't give away too much. Speaking to Deadline, he would only reveal that Sadie's father will have a more significant role to play in Season 5.
The doctor becomes an important character next season to Kevin – he’s having twins with a virtual stranger, not a normal birth experience. It’s no coincidence he was introduced in the same episode that Dr. K returned.
But fans should note, Dr. K's stories about his children — the one he lost and the one who survived — are important parts of the This Is Us mythos. With Sadie already prominently introduced, it might be that Dr. Mason's daughter will also become part of the larger whole.
Fans will have to settle in and wait to see how she fits into all this when Season 5 comes back in the fall.