You've crossed the line. No one messes with my bunny!
— Max to Trevor, the plant
Phoebe gets to take care of a Venus Fly Trap from school while their parents go to Metroburg. Max, Billy, and Nora, try to steal the Venus Fly Trap. Phoebe accidentally spilled water on the Venus Fly Trap and it dies. Max brings it back to life. The things that Max put on to make the Venus Fly Trap made it grow continuously.
Phoebe brings home a Venus Fly Trap plant to take care of it during the weekend for her science teacher. When she shows off the plant to Max, Billy and Nora, they find it impressive how it feeds on flies. Phoebe tells them to not touch the plant because it's on a special diet of flies and rationed water but Max steals it to perform experiments on it.
Phoebe gets the plant back but Max enlists Billy and Nora to come up with a plan to steal the plant back. So, Phoebe must spend most of her time trying to protect the plant from her siblings.
Barb and Hank leave Phoebe and Max in charge so that they can go to Metroburg for the will reading of Barb's old uncle Wilfred aka, "All American Blob." Hank asks the kids to get along while the parents are gone for the night.
For dinner, Phoebe names the plant Trevor as she feeds it its required amount of water and promises not to leave its side. But she is quickly distracted when Nora shouts that Cole Campbell is on the phone. Phoebe picks up the phone only to realize she was being tricked by Billy and Nora so that Max can steal the plant. She quickly stops Max from taking the plant to Max's Lair for experiments. She warns them against feeding Trevor but Nora says that he looks more like a Fernando and so she will feed Fernando! She takes the plant with her to her bedroom. Max then gets Nora and Billy to dress up as ninjas to sneak in and steal the plant from Phoebe's bedroom but she catches them red-handed.
As Phoebe argues with Max about dragging Billy and Nora into this, the Thunder Monitor] announces an incoming transmission from their parents. The kids jump quickly on-to the couch for the video chat. They lie to the parents that they're watching family-friendly movies together and definitely not fighting. The parents wonder why Billy and Nora are dressed up as if they're going to rob a museum, but Phoebe claims that they're mourning the uncle's death.
Phoebe gives Trevor one more drop for dessert before reading him a bed-time story. Unfortunately, the rest of the water spills into the plant pot. This causes the plant to fall. Phoebe freaks out and rushes the plant to Max for help only to find Max plotting with Billy and Nora how to steal the plant and go hide in Cleveland. Max takes the plant to the lair. He dresses up as a doctor and gets Billy and Nora in costumes too. He then makes Phoebe promise that if he brings Trevor back to life, she will let him feed him whatever he wants. Phoebe, having no choice, agrees to Max's demands. Max runs his science magic and revives the plant. Phoebe happily goes to bed.
Early the following morning, Phoebe is woken up by plant leaves touching her. She realizes that it's Trevor. Trevor has grown bigger and his mouth is even bigger. Trevor tries to bite Phoebe. Phoebe freaks out and loudly shouts out for Max.
Max goes to his lair to find Trevor has grown huge too and asks Dr. Colosso how it happened. Colosso blames Max for feeding the plant a lot of things include a ham and a gallon of growth hormones. The plant swallows Dr. Colosso, making Max angry. Max tries to freeze the plant only to realize that it is immune to powers. He praises himself for creating such an evil plant. He still gets scared and runs away into the kitchen. He promises Colosso that he will come back to save him. Max finds Phoebe, Nora and Billy in the kitchen without breakfast because he took all the food to give to Trevor. They ask him if he got Trevor back to normal but he asks for a chainsaw. Before wondering why he needs a chainsaw, Trevor grows out of Max's lair and grabs Billy's foot. Phoebe, Max and Nora start pulling Billy from the plant.
Right after rescuing Billy from Trevor, the parents call again to check in. The kids panic and rush to the couch. The parents wonder why the kids are sitting in the exact same position. The parents are called back to continue listening to the long eulogy. After learning that they can't stop Trevor with superpowers, Phoebe comes up with a plan which involves dressing up Max and Billy as sunflowers to distract Trevor while she grabs the antidote. Sunflower!Billy starts flirting with Trevor while Max shows Phoebe which chemicals to grab. Trevor gets tired of flirting with Billy; so he captures both Billy and Nora. Max puts the antidote on Phoebe's favorite shoe and throws it at the plant. Trevor refuses to take the bait. Phoebe then takes Max's show and beats Max with it for destroying her favorite flats.
Nora realizes that she's about to die and apologizes to Billy for using his toothbrush on Dr. Colosso. This gives Phoebe an idea. Since the plant ate a rabbit, it will probably eat Dr. Colosso's rabbit doll. Max applies the antidote on the rabbit and throws it to Trevor. Trevor eats it and spits out Dr. Colosso, and everything else he had eaten. He then shrinks back to his normal original size. Max and Phoebe start fighting about who saved the day.
The Thunder Twins ask Billy and Nora to act normal when the parents come back. But of course Billy accidentally reveals that they almost got eaten by a giant plant. Phoebe shuts him up before the parents pay any attention to it.
Hank and Barb are excited for Uncle Wilfred's will reading because he said he will give them the most precious gift. They're hoping for a yacht or a mansion. They're shocked when All American Blob's sidekick, Cousin Blobbin is invited for the will reading. They're even more shocked to find out that Uncle Wilfred left all his money, mansion, yacht and his entire fortune to Cousin Blobbin. Wilfred's will claims that the Barb already have the best gift: family. The Thundermans are disappointed.
- Jack Griffo as Max Thunderman
- Kira Kosarin as Phoebe Thunderman
- Addison Riecke as Nora Thunderman
- Diego Velazquez as Billy Thunderman
- Rosa Blasi as Barb Thunderman
- Chris Tallman as Hank Thunderman
- Dana Snyder as Dr. Colosso (voice)
- Cousin Blobbin goes on to become a recurring character on the series in future episodes. The wealth he inherited in this episode are also a big part of his future plotlines.
- Max dressed Billy and Nora in ski masks again in Dog Day After-School
- Max being a science "genius" in this episode becomes a common theme in multiple episodes including Weird Science Fair.
- The plant can be likened to Audrey 2 in the 1986 musical Little Shop of Horrors.
- This marks the first appearance of Phoebe's room.
- This episode is aired as the first part of a Double Thunder night on Nickelodeon.
- This episode got 2.0 million views.
- This is the first appearance of Cousin Blobbin.
- Billy knows how to flirt with plants
Max: Come on Phoebe, it's been my long life dream to see a plant eat weird stuff
— Max and Phoebe
Phoebe: Max, I can't believe you dragged Billy and Nora into this.
— Phoebe and Max
The image gallery for The Weekend Guest may be viewed here.