'Welcome to Plathville': Kim Plath Surprises Her Kids After a Difficult Year in Finale Exclusive Preview

It's been a difficult year for the Plath family, but mom Kim Plath is determined to end things on a high note at home. In PopCulture.com's exclusive Welcome to Plathville season finale preview, the mother of nine attempts to pull off a "fun prank" for the family to raise spirits amid tension with older children Ethan, 22, Micah, 19, and Moriah, 18, over their conservative upbringing.

Keeping her plans to herself for the time being, Kim asks daughters Lydia, 16, Amber, 11, Cassia, 9, and Mercy, 7, as well as 14-year-old son Isaac, to get all dressed up in the "fanciest dress [they] can find" and prepare for a special Plath family dinner. (Kim is also mother to 21-year-old daughter Hosanna).

"I have something very special and very unique planned for this evening, and I'm the only one that knows about it," she teases the camera. "I've had so much fun planning it — how to arrange the tables so that I can pull it off."

Promising Lydia that the "sky is the limit" on what dress she can wear, Kim admits to the camera that there's more than just a nice dinner coming the kids' way: "It's something I've wanted to do for a long time, but everything has to just line up perfectly ... including the weather."

When the kids do come down in their nicest clothes, Kim instructs them to sit at their marked seats at a table set up outside and prepare for a delicious meal of shrimp, spanakopita ... and pie. No one in the family has any idea of what's to come, with Lydia asking her younger siblings if they are thankful for the big night, and father Barry Plath answering, "I'm thankful." He continues of the meal, "This is great. It's not often we just decide to do it up fancy do we? Plathville's five-star restaurant."

The family enjoys their dinner unhindered until Kim reveals there's still a bit of dessert to be had, bringing a pie in front of Isaac's face and asking him to inspect it before smashing it into his face. After a moment of shock, the family erupts in laughter, and Kim reveals there are plenty of pies for everyone to get in on the action, resulting in a family-wide pie fight.

Kim shares in a confessional later that while the struggles with her older children have taken a lot out of her this year, she wanted to make sure her more fun side still had an opportunity to shine."You wouldn't have seen me pull a fun prank, you know, in the last year, just because of all of the drama going on and how heavy that's been on me," she says. Don't miss the Welcome to Plathville season finale, airing Tuesday, Jan. 5 at 10 p.m. ET on TLC.