In an exclusive first look at This Is Us' season 4 fall finale, Randall and Rebecca find themselves in another argument

Though Randall (Sterling K. Brown) has nothing but his mom Rebecca (Mandy Moore)’s best interests at heart, he can’t help but assume something is off with her when she comes to Philadelphia for Thanksgiving.

PEOPLE has the exclusive first look at This Is Us‘ season 4 fall finale and the mother-son relationship remains unsteady.

Last week, fans saw Randall and Rebecca get into a heated discussion about her mental well-being after she temporarily misplaces her new cell phone and exhibits behavior that leads to the councilman worrying about possible memory loss.

And on Tuesday, viewers will find Randall and Rebecca in another argument before the rest of their family arrives for dinner. When the Pearson matriarch goes to turn on the kitchen stovetop, her son quickly turns the flame off due to his assumption that she’ll have a memory lapse.

“Randall, I did not forget,” Rebecca, who remains defensive, tells her son after she caught him turning off the stovetop. “I was just going to make myself some tea … You know, I also managed to make the cranberry sauce this morning without blowing up the house.”

“Mom, I didn’t mean to overstep last night,” Randall says, referring to their argument.

“I really want to put last night behind us,” Rebecca tells him before her son reminds her again: “But at some point, we need to talk about out what’s going on with you.”

Mandy Moore, Sterling K. Brown
Credit: Ron Batzdorff/NBC

Now, Rebecca is frustrated and fed up. “Okay, I need some space. I’m just going to take a walk, clear my head,” she says. “I’ll be back in time for dinner.”

But not before she asks Randall to keep their conversation a secret. “I would appreciate it if you kept this argument of ours between us,” she says.

Audiences will recall the fall finale teaser previewing Rebecca appearing lost and confused during her walk. Is this another “senior moment” or perhaps a sign of dementia or Alzheimer’s? Or is she just lost since she’s not in Pittsburgh?

This Is Us airs Tuesdays (9 p.m. ET) on NBC.