The episode begins as SpongeBob is feeding Gary. He accidentally drops the food and chaos ensues. Then, SpongeBob goes off to work. Gary tries to come with him but SpongeBob cannot bring pets to work and leaves Gary at home. Gary then turns on the TV, uses his leash as a lasso to grab a cowboy hat in a cupboard, and watches a cowboy show or movie. A customer comes in with his pet worm Jan. SpongeBob explains that people cannot bring their pets. The man is just about to leave when Mr. Krabs came and told him to buy Krabby Patties. He says to the man that he is a responsible pet owner. Then, SpongeBob feels guilty for leaving Gary alone after what Mr. Krabs says, and decides to call Gary. Gary is too busy watching TV to answer the phone. SpongeBob thinks he is too sad to answer. SpongeBob then listens to the message on the answering machine. It is a message that SpongeBob and Gary made that talks about SpongeBob and Gary having fun, this makes SpongeBob feel even guiltier. He then leaves a message saying that he knows that Gary is feeling lonely and that he will be home soon. While this is happening, Gary is watching TV and having a good time.
SpongeBob flips the "open" sign to "closed." He sneaks out of the Krusty Krab hoping not to be noticed so he can just go home without doing any more work. However, this is stopped when Mr. Krabs notices him closing the door to the Krusty Krab. Mr. Krabs is seen covered in tar and holding a shovel. He is next to a tar maker about to retar the parking lot. He asks SpongeBob to join him and SpongeBob declines. Mr. Krabs understands and tells him to come to work 5 hours early to finish the parking lot. He spots a stand with Nudibranchs. SpongeBob sees a green one with purple eyes, huge pink lips and blue fins. He says he wants it, but an old peddler woman (she owns the Nudibranchs) warns him that looks can be deceiving because they are violent and dangerous, especially around other animals. SpongeBob ignores her warning and takes it home anyway while the old peddler woman says to herself that the people never listen.
When he gets home, Gary is still watching TV. SpongeBob gets in front of the screen to show Gary his new friend, which he named "Puffy Fluffy," then leaves to make enchiladas. While in the kitchen, Gary is chewing his toy in front of Puffy. It is then shown that the peddler's warning was right as Puffy then growls and scares Gary to go behind the couch while Puffy chews his toy apart. Puffy, about to bite Gary, sees that SpongeBob is coming back and turns himself back to a nice Nudibranch. SpongeBob gets Gary's bowl and makes a slash on it with marker. On the other side of the slash, he writes "Puffy Fluffy." Gary starts to eat when Puffy Fluffy Growls at him again. Then Puffy eats every single piece of food in the bowl. SpongeBob sees that Gary is hiding from Puffy again, and scolds him. Gary then jumps on SpongeBob while Puffy looks like he has absolutely no idea why Gary is on SpongeBob.
At bedtime, SpongeBob tells Gary he is going to sleep with Puffy Fluffy tonight. When he puts Gary in the bed, he hisses at Puffy. As SpongeBob is about to go to sleep, Gary bursts in, scared about Puffy Fluffy, but SpongeBob takes him back downstairs, seeing this as Gary thinking his friend is mean. He puts Gary back in the living room and tells him to let him sleep, before going back to bed.
Some time later, Gary wakes up and sees Puffy's skin on the bed. He walks in the kitchen to see a huge eel eating in the refrigerator. The eel is revealed to be Puffy Fluffy, who now has five tongues with a mouth on each. Puffy then attacks Gary and SpongeBob does not wake up throughout.
In the morning, SpongeBob wakes up and discovers the damage to his library. He assumes it was Gary who did it because he's jealous about the new friend. After bursting through the door downstairs, he finally sees Gary is about to be eaten. Gary is relieved, only to be shocked when instead of helping him, his owner starts to scold him for his destruction and how he's still treating Puffy Fluffy, even when the eel is clearly about to eat him. SpongeBob continues to lecture Gary until Puffy Fluffy's tongues grab onto SpongeBob, who's still scolding his snail even as he's about to be eaten. Using a leash as a lasso, Gary whips at Puffy Fluffy, driving it away from SpongeBob's pineapple home. SpongeBob chases after the beast crying for it not to go, then turns and admonishes Gary for chasing Puffy Fluffy away, to which Gary gives an annoyed glare.
Later on, SpongeBob brings Gary to work, so he is not lonely, and then Mr. Krabs gives Gary a spatula to help work. Gary meows in a disappointed tone.
Mr. Krabs told SpongeBob to come in five hours early at work, so he should have woken up at 4 a.m. instead of 9 a.m.
SpongeBob should have known better than to scold Gary when he was about to be eaten, especially since his pet was in a life threatening situation. Likewise, he should have listened to the woman's warning about Fluffy, should have been frightened by Fluffy's mutation, and should not have yelled at Gary at all when he himself was about to be eaten and when Fluffy ran away, otherwise, he would not have put his pet in such danger.
It's unknown why the fire log was lit in SpongeBob's library, when SpongeBob SquarePants was sleeping in his bedroom and there was nobody to watch over it. Monstrous Puffy Fluffy makes it even worse when he uses his tail to kick the lighted fire log away from the fire place, it lands on a pile of books, and sets the library on fire.
In addition to this, who lighted fire log in the first place?