After 17 years, Egon Olsen is placed at the Institute for Theoretical Crime, a psychiatric institution for incurably criminal persons. He had left the institution for the first time to participate in a TV talk show. Benny, who works in black for a taxi company, and Kjeld, who sits in a wheelchair and lives in a nursing home after Yvonne's death in 1987, both saw the broadcast and decide to visit Egon at the studio.
Outside the studio, Egon desperately seeks a toilet, and on the street he runs into Benny Fransen. The two old partners reconnect and decide to seek out Kjeld at the nursing home, hoping to reunite the gang for one last big score.
Egon unveils a renewed, long-simmering plan to raise the capital the Olsen gang needs. During his lengthy time in psychiatry he has drafted countless schemes, most of which were confiscated by the superintendent and locked away in a safe. This time his target is audacious: the English crown jewels.
The broadcast somehow reaches more than just old enemies. Hallandsen, the department head at the Ministry of Justice, recognizes Egon and sees a fresh opportunity to settle old scores. The risk is high because a suitcase containing the top-secret Wandenberg documents—the dossier that would reveal decades of public scandals—could become public knowledge. A failed early attempt to swipe those documents from the Foreign Affairs archive haunts the authorities, and the live TV appearance only intensifies the pressure to prevent another breach.
Holm-Hansen is tasked with tracking Egon down, while the detective assistant Jensen—who, it’s joked, should have retired long ago but was kept in play by a computer error—advises targeting the last Franz Jäger safe from 1944, the remaining key to the Department of Theoretical Crime. The search accelerates as Egon, back at the institute, plots to steal his own plans from the safe. The headmaster blocks him, but Holm-Hansen intervenes and extracts Egon, allowing Kjeld and Benny to slip away unseen.
Egon is brought to Hallandsen, who assigns him the mission of stealing the Wandenberg documents, promising a reward for success. With the help of two ministry officers, Egon quickly breaks into the system and makes off with the documents in a matter of minutes. Yet the reward outcome backfires: Egon is locked in a dungeon in the Ministry of Justice, where he is attacked by Bøffen and his henchman Alf. Kjeld and Benny mount a daring rescue just in time to pull him free.
Hallandsen wants to destroy the suitcase with the Wandenberg documents at the state-of-the-art destruction facility, but Egon sees a better, more dangerous option: keep the suitcase and use its contents to blackmail Hallandsen. Together with Benny and Kjeld, he stages a risky operation to reclaim the suitcase, employing improvised tools—a boat hook, dish soap, and other clever makeshift devices—to outwit the security forces and seize the documents once more. The required bolt of shock leaves Hallandsen rattled as he drives away in disbelief, while Bøffen and Alf threaten to strike again.
The trio heads toward the Øresund connection construction site, intending the handover to take place there. Ruth unexpectedly joins the ride, substituting for Kjeld who isn’t feeling well, and Egon reluctantly accepts her presence as part of the plan. At the construction site, the group is ambushed again and dragged into a cave beneath the earth, where they must protect the Wandenberg documents and Egon’s plans from being lost or destroyed.
Meanwhile, Kjeld’s family is drawn into the drama. Kjeld’s son Børge arrives from abroad, a successful international company manager who is eager to find his father and learn what has happened. The reunion adds a new layer of tension as the stakes rise and the group presses forward toward a resolution.
In a pivotal moment, Ruth and Alf push the suitcases onto a construction machine, scattering Egon’s plans and the Wandenberg documents, and vanishing from sight. Hallandsen, reeling from the turn of events, makes a frantic bid to escape toward Jutland, while Holm-Hansen effectively steps into a new leadership role in the aftermath.
In the final act, Egon, Benny, Kjeld, Ruth, and Alf set out for a quieter life at Børge’s villa in Portugal, hoping to leave the past behind. Yet even as they seek peace, Egon’s old ambitions endure, and the dream of one last coup—stealing the crown jewels—lingers just beneath the surface, a reminder that the mastermind behind the Olsen gang never truly retires from crime.
