This Is Us Season 6 episode 1 revolves around the themes of growth and loss.

In the present, Rebecca is upset when she can't remember the word "caboose" while telling Jack a story from her childhood and continues to push herself to remember the word. It stops her from enjoying the Big Three's 41st birthday, and after her frustration causes her to have an angry outburst, she has to tell her kids the sad truth: her PET scan shows plaque building up in her brain.

Meanwhile, in 1986, Rebecca and Jack worry about the kids after they watch the Challenger liftoff in school and see the rocket explode. Kate seems the most okay with the news, telling Rebecca and Jack that the astronauts were closer to heaven because they were up high, while Kevin and Randall both seem to shut down. Rebecca worries that she hasn't dealt with this right and that it will scar the kids for life, but Jack doesn't think so.

Elsewhere, Kevin has some big decisions to make, especially after realizing that Madison has already started to move on, and Randall discovers compassion for the man who robbed and terrorized his family two years ago.

To find out what happens, watch This Is Us Season 6 Episode 1 online.