In preparation for her birthday celebration, the Smurfs read the story of Smurfette, how she was created by Gargamel to destroy them, only for Papa Smurf to rescue her and turn her fully into a Smurf. Meanwhile, she is having nightmares about reverting to her original form and betraying her fellow Smurfs by turning them over to Gargamel. The Smurfs are preparing a surprise party, but as Smurfette tries to find out what her fellow Smurfs are planning, none of them are saying a word. She takes this to mean that everyone has forgotten her birthday.
In France, Gargamel is now a celebrity, amazing people with his sorcery, but he sees that he is running low on the Smurf essence that gives him his magic powers. With his new creations, evil Smurf-like creatures called Naughties named Vexy and Hackus, Gargamel plans on opening a portal to the Smurf village by using the Eiffel Tower as a conduit so that he can kidnap Smurfette and, through her, get Papa Smurf’s secret formula for creating Smurfs. However, as the portal he created is not big enough for him to go through, Gargamel sends Vexy through to the portal to grab Smurfette and bring her to Paris.
The Smurfs witness the abduction of Smurfette and inform Papa Smurf, who uses his magic to create crystals that allow several of his Smurfs to travel directly to Patrick Winslow’s residence in New York City in order to get his help to rescue Smurfette. Papa originally intends for Brainy, Hefty, and Gutsy to use the crystals, but through an accident, Clumsy, Grouchy and Vanity use them instead. Papa and the three Smurfs arrive in the apartment right after the celebration of Blue’s fourth birthday where they meet both the Winslows’ young boy and Patrick’s stepfather Victor Doyle, a man who is a constant embarrassment to Patrick. The Smurfs soon discover where Gargamel is, and so they and the Winslows set off for Paris in order to find him.