Eloise (Anna Kendrick) gets dumped by her boyfriend Teddy (Wyatt Russell) a few days before Teddy's sister's wedding. She gets bumped to table 19, where she sits with Jo (June Squibb), Teddy's former nanny with terminal cancer; Rezno (Tony Revolori), a lonely teenager; Bina and Jerry (Lisa Kudrow and Craig Robinson), an unhappy married couple; and Walter (Stephen Merchant), who is on parole after a robbery.
During the wedding, Eloise hits it off with Huck (Thomas Corcqeuel), who wasn't even invited to the wedding. Teddy sees them kissing and get mad at her and asks her to leave.
Soon after, Jo realizes that Eloise is pregnant with Teddy's baby and that was why he dumped her. Jerry also finds out that Bina came to the wedding to have an affair with an old friend. The group leaves the wedding and Eloise tries to find Huck, but sees him marrying another woman in the same hotel.
While everyone is upset, Teddy's sister Francine (Rya Meyers) comes to table 19 and personally thanks everyone for coming. She also tells Jo that Teddy gave a gift that she bought for him to her when she was upset. Jo then tells Eloise that she should go after Teddy, while Bina and Jerry make up.
Eloise goes to tell Teddy that she loves him, but he is on the ferry with the Francine and can't hear her. Defeated, Eloise goes to the wedding hall to have cake, but is surprised by a soaking wet Teddy who kisses her.