Follows the family lives of Kevin, Kate, and Randall, who are also known as "The Big Three" and share the same birthday, in present time, while revealing their connection to married couple Jack and Rebecca Pearson, who are about to become parents of triplets on Jack's 36th birthday in 1980 in Pittsburgh, Pennsylvania, USA.

After a devastating loss of a member of his family and a nervous breakdown, Randall decides to change all their lives by making some bold decisions in order to honour the legacies of his father(s). Kate finally decides to pursue a career in singing, supported by her fiancé Toby, which will put their relationship to the test. Meanwhile, Kevin is reunited with his first love Sophie and about to become a huge movie star, until the ghosts of his past catch up with him. Turns out that "The Big Three" depend on Jack and Rebecca - in more ways than they allow themselves to admit it.