Villagers unearth a Fangpyre skeleton, and after observing it, Kai, Cole, and Zane head off but Jay stays behind with Nya. He asks her out on a date, to which she accepts. When Jay pricks himself by accident on the Fangpyre skeleton's fang, the venom gets on his hand and begins to turn him into a snake.
Meanwhile, in the Dark Realm, Sensei Wu tries to talk with Lord Garmadon about Lloyd and how he got captured, but Garmadon doesn't listen and they have a fight. Garmadon uses a double-bladed spear, a scythe, a staff with a shuriken attached, and a regular staff, while Wu uses his katana from their youth. Wu attacks but Garmadon counters with all his weapons and forced Sensei off the ledge they are on. Sensei falls in the mud, and Garmadon calls his Mud Monsters. Sensei uses his Spinjitzu on them to knock them out, but Garmadon sends more. Garmadon uses the Mud Monsters' special move, Converge. They all come together and overwhelm Wu. Sensei barely pokes his head out of the mud coverage to inform Lord Garmadon that Lloyd is in danger. Sensei Wu sinks in but Garmadon grabs him and pulls him out. Garmadon asks what Lloyd has done and Sensei explains. Garmadon agree to go back to Ninjago to help Lloyd, temporarily forming an alliance. Wu tells him that he's out of Traveler's Tea, so Garmadon informs Wu that the only way to get back to Ninjago is to climb the very dangerous Mountain of Madness.
Pythor and the Serpentine head off to Mega Monster Amusement Park to dig up the first Silver Fangblade. The Ninja find out that the Serpentine are at the amusement park, so Jay arranges the date there so he can fight and have the date. During Jay and Nya's date, Jay finds out he is turning into a snake due to the bite and heads towards the restroom. Meanwhile, the Ninja go to the ghost ride, where they find the Serpentine who have already dug up the first Fangblade. Zane accidentally freezes the three of them while he is in NRG mode, which allowed the Serpentine to escape.
When Jay comes out of the bathroom, he can't find Nya (who has assumed her identity of Samurai X). The customers of the restaurant think Jay is a snake due to him turning into a Fangpyre so they attack him. Jay goes to the bathroom and comes out with a scarf on his face so he can escape.
The Serpentine had already revealed Samurai X as Nya and chained her to a roller coaster which had heavily damaged tracks. Jay gets on it to help her. On the coaster, Jay reveals he's turning into a snake and Nya reveals she is Samurai X. When Nya kisses Jay, he turns back into a human. He then unlocks his True Potential and saves them. At the end, the Ninja and Nya gather and wonder where Sensei Wu is and what he's doing. Meanwhile, Lord Garmadon and Sensei Wu have reached the Mountain of Madness and prepare for their journey.
The name of the episode is a reference to the phrase "once bitten, twice shy," referring to how people tend to become more reluctant to pursue a relationship after the failure of a previous one.
In the context of the episode, the title is more of a double pun; Jay is infected with Fangpyre venom after pricking his finger on a Fangpyre's fangs, and he tries to impress Nya because he fears that she won't appreciate his natural personality.
This episode marks the beginning of Jay and Nya's relationship. It also marks the last time Nya uses her "Samurai X" identity - although she will still use her technology, it will be under her own name.
As of this episode, the entire known Walker family has been infected with Fangpyre venom at some point - previously, Jay's parents were bitten by Fangpyre in "Snakebit."
Jay's Fangpyre infection appears to progress slightly differently from his parents'; his hand begins showing a green tint and scale textures before he begins developing fangs or a hissing voice. This may be due to his infection starting with a pricked finger, as it is never shown or mentioned where Ed and Edna were bitten in "Snakebit."
The Fangpyre skeleton appears to belong to a General, possibly Fangtom's predecessor.
