With the help of an origami wedding predictor that she has filled out with the names of her classmates,Rhonda claims to infallibly predict who whill marry whom. She then predicts that Arnold will marry Helga when both grow up, much to Arnold's dismay and Helga's secret triumph. A heavily affected Arnold spends several hours trying to get a different outcome, to no avail, which is interpreted as the inevitability of his marriage to Helga. The idea causes such a heavy impact on each of them that they both have dreams in which their interpretation of said marriage plays out that very night.
Helga dreams of an elegant, romantic church wedding in which a muscular and dreamy Arnold and she wed, after which they go to Venice for their honeymoon. As they travel the canals on a gondola, a bedraggled Lila Sawyer appears, begging that Arnold love her back again, to which he responds that he loves Helga (Lila's gondola promptly sinks). They live a dreamily happy life, in the midst of which Helga decides that she wants to run for president: she wins the elections, even letting Arnold have a few seconds for himself during her acceptance speech (after which he is promptly elbowed out of the way). Helga proceeds to deal with presidential duties, with an adult Phoebe as her secretary, never hesitating to axe every compromise to let Arnold in to see her or have a pastrami sandwich. As she attempts to come to a compromise with Switzerland over the phone late at night, Phoebe bursts in to tell her Arnold has been kidnapped by a mysterious organization, and is prepared to send out the rescue team when Helga insists on rescuing him herself. With Phoebe guiding her via comlink, Helga breaks into the enemy fortress, battling ninjas and breaking through convoluted security measures until she reaches the control room, where Arnold is tied to a chair. She then briefly battles the masked organization leader, who, once defeated, turns out to be Lila. Failing to win Arnold's heart, Lila concocted the kidnapping to make one last attempts at making him love her again, though she is now profoundly sorry. After Arnold once again says his only love is Helga, the US Special Service (led by an adult Gerald) arrives to arrest her for kidnapping Arnold, and the reunited couple romance on a hot air balloon.
As Helga lives her fantasy, Arnold is having a nightmare: he appears at church and is told by Gerald that he is no longer nine (he is 25, and appears tall) and that he is there to be married with the woman he fell in love with. As he is told of this, a veiled bride walks up to him, revealing herself to be Helga, to his horror. Arnold attempts to resist (even as an adult Rhonda shows up with the origami wedding predictor, on which only Helga's name is visible to him), but is finally tricked into saying "I do" by Helga. He is then dragged to his new home, the Pataki household, where Big Bob informs him of his new job at Big Bob's Beepers to maintain his new wife, who proceeds to spend all day in front of the T.V, snacking. He is expected to work as an unloader, a heavy duty job that feels worse when accidents keep stopping him from safely unloading the boxes. As Arnold and his new father-in-law are coming home from an awful day at work, Big Bob points out a stork flying over the house: a load of bratty, misbehaving babies has been delivered to them (after having been married for only two days), all of which are left entirely to Arnold's care, despite the fact that he must also go out to work. After arriving home the next day (as it appears in the dream's continuity) to the babies ravaging the house as an insolent Helga watches on, Arnold decides he has had it: he grabs Helga angrily, telling her that if they have to be married, things have to change. He declares that he will quit his job, that they will move out of the house and find a new place, that she will have to have her share of responsibilities and, most importantly, she will have to show him some respect.
As the Pataki house fades around them, Arnold seizes Helga, telling her that he knows she isn't "that cold, lazy and uncaring", urging her to show her "good" side. Her ruse exposed, Helga breaks down and accepts that her outward aggressiveness hides a softer interior, and that Arnold alone has seen through it (it is important to note that this speech by dream-Helga is identical to the one the real Helga had been delivering behind a trashcan earlier that same day, implying that, despite his denial, Arnold did hear her). As Helga is about to confess that she does love him, his alarm clock rings, and the dream ends.
That day, Arnold recounts his dream to Gerald as they travel on the bus home once again. He doesn't deny that the beginning was pretty awful, but he also admits that Helga turned out to be a good person in the end and that, whilst he is only 9 and has plenty of time to decide who he'll marry, a marriage to Helga wouldn't be that bad. Helga, who is crouching in the chair behind them, is pleased to hear it. At that moment, Rhonda climbs onto the bus and publicly declares that she has found the marriage predictor to be faulty, making all her predictions false. She apologizes to Arnold for the fright she feels she must have caused him, as it was his marriage prediction which made her think the origami marriage predictor faulty. She comments to Phoebe on the unlikelihood of the couples she'd predicted, asking her if she could ever imagine Arnold and Helga together. Phoebe says nothing, but smilingly imagines an adult Arnold and Helga holding hands atop a lighthouse watching the sunset, marriage rings on their fingers.