As Allan Karlsson celebrated his momentous 101st birthday on the sun-drenched beaches of Bali, an unexpected event was brewing. An intense discussion erupted between Miriam and Julius regarding the last bottle of Folksoda, a quirky soda that Allan concocted during his secretive days as a double agent in the 1970s. Meanwhile, with a mischievous glint in his eye, Allan's pet Erlander, a Capuchin monkey, took advantage of the distraction and gulped down the elusive drink, leaving astonished spectators behind.
Later, after saying their goodbyes to Allan, Julius, and Gäddan, Miriam and her husband Benny made their way back to Malmköping. The remaining trio decided to stay at the resort, where Allan revealed a shocking twist: the last Folksoda had mysteriously disappeared, but the treasured formula was safe, tucked away in a cigar box at Amanda Einstein's apartment in Berlin. Seizing the moment, Allan immediately called Amanda, eager to retrieve the prized recipe.
Together, Allan, Julius, and Gäddan thrummed with anticipation as they prepared to head to the airport, unaware that fate had plans of its own. While they flew high above the landscape, little Erlander managed to escape from his carry-on bag, leading to an unexpected emergency landing in Moscow. This bewildering incident caught the attention of Rebecca, a stewardess who inadvertently let the crafty monkey slip away.
As the news of Julius and Erlander's antics went viral, capturing audiences worldwide, Stirna, a woman burdened by her past, uncovered Allan's true nature through her own investigations into the viral phenomenon. Recognizing him as the thief who had stolen the formula from her deceased father, Popov, she persuaded her therapist, Håkan, to assist her in the chase for Allan.
The city streets of Moscow transformed into a maze for the duo as they pursued their target. In a twist of fate, Bas, Rebecca's husband, uncovered that Allan was actually the cunning criminal responsible for swindling Pim out of 50 million dollars. Seizing this opportunity, Bas prepared for confrontation, armed and ready to track down Allan.
Eventually, the authorities intervened, releasing Allan and his companions, while Erlander remained quarantined, awaiting inspection. Reflecting back on his past during a Folksoda film shoot in East Germany, Allan remembered meeting Popov's young daughter, Kristina. Stirna cleverly manipulated local authorities into releasing Erlander in exchange for the secret formula.
Upon their arrival in Berlin, Allan and Julius were met with tragedy as they found Håkan dead, a casualty of a champagne cork disaster. As they traveled by train towards Berlin, accompanied by Stirna and Bas, tensions ran high, and they were unaware of the perilous journey ahead that would unearth Allan’s shadowy past.
Within Berlin’s dynamic streets, Amanda was reminded of a wild 1970s rave where Allan, still reeling from LSD, had once impulsively tattooed the recipe for Folksoda on his left buttock. Meanwhile, Benny rushed to Allan's old nursing home, eager to track down his possessions and replenish his Folksoda stash. Unfortunately, both Stirna and Allan were disheartened as they scoured through an old cigar box only to find it loaded with plain cigars.
Just as events seemed to take a darker turn, Inspector Aronsson and a couple of CIA agents appeared at the nursing home. Their questioning was abruptly interrupted by Benny’s anxious bout of vomiting. Unfazed, Allan and Julius set off on a clandestine mission to uncover the truth behind Allan's missing belongings, only to find that they had mysteriously vanished.
Determined, Allan, Julius, Gäddan, and Stirna banded together to rescue the cigar box from destruction at Benny's home. In a nail-biting sequence, they successfully reclaimed the microfilmed formula, allowing them to breathe a sigh of relief amidst the chaos.
As the dust began to settle, Stirna unveiled her true identity as Kristina, Popov’s daughter, earning Allan’s trust with the formula before they parted ways. However, that moment was cut short as Bas appeared, gun in hand, demanding everyone's focus. In a tense showdown, Allan surrendered the stolen loot from Pim, only for Bas to meet a tragic end at the hands of Inspector Aronsson.
In a surprising twist, Julius stumbled upon the revelation that Allan's tattoo housed a Russian transcription of the original Folksoda recipe. Fast-forwarding to the present, Miriam and Benny hosted a joyous gathering to mark their newborn, Allan Jr., bringing warmth to the scene.
In a heartfelt gesture, Stirna chose to remain with her new companions, joining Julius in the journey to recreate Folksoda. However, they soon discovered a vital step was missing from their endeavor. Just as Allan settled down with friends to enjoy a well-deserved meal, nature unleashed its wrath – a sudden bolt of lightning struck, igniting a fire that uncannily resembled one from the past, leaving the group in stunned silence.
