'This Is Us' season 1 episode 17 spoilers: Randall celebrates William's life in an unusual party, Rebecca leaves her family to go on tour

The Pearsons gather at Randall's (Sterling K. Brown) house on the upcoming episode of NBC's gripping family drama "This Is Us."
Titled "What Now?" next week's episode will center on an unusual party. According to the official synopsis, all members of the Pearson family head to Randall's for an out-of-the-ordinary party. On the premiere night of Kevin's (Justin Hartley) play, he and Sophie (Alexandra Breckenridge) grow closer to each other. Kate (Chrissy Metz) finds it difficult to open up to Toby (Chris Sullivan) about her father's loss, while Jack (Milo Ventimiglia) and Rebecca (Mandy Moore) get in a heated argument when she leaves with her band for a tour.
NBC released a new trailer for the episode, and it opens with Randall's party. The teaser reveals that Randall organized the gathering to celebrate his father's life. "He changed me," Randall says, adding, "I loved him." The next scene cuts to Kevin having a conversation with Sophie about his brother. Sophie is also there to support him on the first night of his play.
At some point in the video, Rebecca says goodbye to her family as she goes on tour with her band. "I'm leaving. Take care of each other," she tells her kids while hugging Kate. The promo wraps up with Jack heading to a bar where he appears to be attracted to the female bartender.
Following Tuesday's devastating hour, series creator Dan Fogelman talked to Entertainment Weekly to share some teasers about the next episode. He teased that episode 17 will see a different side of Randall as he tries to cope with his father's death.
"I think you'll see a lot of that in our next episode, and then really bleeding heavily into next season," he said. "He's clearly a man who's lived a very structured existence, and he's a man who's all things to all people... He starts making a bunch of choices and decisions that will affect us going into season 2," he went on to say.
"This Is Us" airs every Tuesday night at 9 p.m. ET on NBC.