The episode starts with Papa Smurf taking a walk with Grandpa around the village when they see Joey getting out of Hefty's house with a basket. He greets them and goes out to gather smurfberries, but Grandpa thinks that it's about time Joey settles into his own "mushroom."
Papa Smurf agrees, so he calls Handy, Hefty, and Architect, and tells them about surprising him. They reject Jokey's offer, and instead Papa calls Moxette - he asks her to stay with Joey and find out what sort of house he would like. She agrees to do so and runs off to find him.
Meanwhile, Joey is collecting some smurfberries when Moxette appears and asks, "If you were looking for a house, what kind would you want?" He answers by saying, "Well, I'd like one with two floors plus an attic and a basement," but when he looks at her, she is gone; he becomes confused.
Back at the village, Moxette tells Papa and the others by mimicking Joey's dialogue. Architect make the design of the mushroom, but he hides when Joey returns. Then Papa Smurf gives Joey a mission to gather some rocks in the "Lock Cave" and asks his little Smurfs to volunteer to go with him. Moxette offers, so Grandpa gives them good luck while touching Joey's shoulder and then they leave.
Joey asks Moxette where the Lock Cave is, so she tells him that it's on the other side of the Smurf forest. When they arrive, they are shocked by what they see - instead of a cave, there is just a waterfall. Joey starts to become suspicious when suddenly he feels dizzy and sees a vision about a silhouetted Smurf with a stick jumping in the waterfall.
Joey tells Moxette that they need to jump into the waterfall, but she refuses because she doesn't want to get wet and potentially hurt, so Joey does it by himself. Moxette watches the water and waits a little for him to return, but out of worry she jumps in after him. To their surprise, the waterfall has a cave inside, so they continue on their mission.
Meanwhile in the Smurf Village, Handy and the other Smurfs are building Joey's house, but it is hard to handle due to Brainy pestering, Clumsy's clumsiness, and Fooly's foolishness. Handy and Hefty do their best to work through the hecktic environment.
Back in the cave, Joey and Moxette walk until they arrive in the central pit where there are many rocks and jewels. The rocks Papa was looking for are unbreakable and used to make fire. They are only found in this place; they notice a big diamond against one wall and, out of curiosity, Moxette tries to pull it out. She fails and says, "I wish Hefty was here - he's strong enough to remove this diamond!"
Joey starts to feel dizzy again and sees another vision of the silhouetted Smurf with a stick who approaches the big diamond. He pushes it and the cave starts to shake and a wave of water appears, washing him out. Shocked by this, Joey is relieved that she doesn't know about that, but then Moxette gives it a little push with her finger.
Joey tries to tell her not to push it, but it's too late: the cave starts to shake and a wave of water washes them away. They end up in a hot spring with fairies, Piximps, and an elder Gnome named Elder Golem. He tells them the waters of the cave always brings the creatures inside to this hot spring, and the diamond is actually a button in disguise.
Back in the village they are finally finished making the house right before Joey and Moxette return from their long journey with the rocks. They surprise him with his new house - a green mushroom with two floors, an attic, and a basement. He loves it, but then starts to wonder about his vision and asks, "Who was that Smurf? All I remember is that he was carrying a stick!" Suddenly he realizes it was Grandpa and tells Papa Smurf that he had a vision where Grandpa was in the Lock Cave before.
Of course no one believes him, but Joey insists, so Papa, Hefty, and Moxette decide to ask Grandpa Smurf about that. When they find him and explain it, he exclaims, "Smurfatooty! I haven't heard about the Lock Cave for years! Yes, I was there a long time ago during my own journey!" They are bewildered and realize that Joey was right.
Later that night, Joey is inside his new house with some souvenirs: part of Clumsy's rock collection, a mini wrestler figurine from Hefty, a sunflower from Smurfette, and a Smurf-lender that was built by Handy. On his bed he wonders why he had that vision, and then falls asleep.
In the Smurf forest, the shadowy figure is flying through the rustling trees and finds an area. He lands and whisper, "Another Time Gear...now I have two! There are three left in order to complete my goal!" Then the screen turns black, thus ending the episode on a suspenseful note.