The epic tale of The Hitchhiker's Guide to the Galaxy begins, rather unassumingly, on Earth as dolphins, heralded by our humble narrator, The Guide (Stephen Fry), as the second most intelligent creatures on the planet, decide to leave Earth before its impending destruction. Their attempts to warn humans of the danger are tragically misinterpreted as sophisticated tricks or amusing gimmicks for tidbits.
Their last attempt to send a message is a suprisingly sophisticated attempt to do a double-backwards sommersalt through a hoop while whistling the Star Spangled Banner, which is in fact their way of saying, "So Long, And Thanks For All the Fish." Arthur Dent (Martin Freeman), an average man living in the English countryside, wakes one morning and dons a robe before running outside in response to the sounds of a construction crew surrounding his home. He lies down in front of a bulldozer to keep it from demolishing his house to make way for a bypass.
The foreman (Mark Longhurst) impatiently informs Arthur that the damage sustained to the bulldozer would be unnoticeable should it run over him. At that moment Arthur's best friend, Ford Prefect (Mos Def), arrives with a shopping cart full of beer. He pulls Arthur from the ground and tells him that they need to leave and have little time to spare since his home is about to be destroyed. Arthur points knowingly to his house which confuses Ford for a second before he assures Arthur that they have some time to buy.
He offers his loot of beer and peanuts to the construction crew and gives Arthur the confidence that the distraction will allow them enough time. He takes Arthur to a local pub where he explains that he is not from Guildford as he'd once claimed. He is, in fact, from another planet in the vicinity of Betelgeuse and addresses Arthur's skepticism with a recounting of their first meeting (Arthur tackled Ford out of the way when he was trying to shake hands with an oncoming car (an actual Ford Prefect), having mistaken cars to be the dominant life form on the planet).
As they share drinks, Arthur pulls out his phone and reminisces over a photo of himself and a young woman at a costume party. Drunk and distraught over the day's troubling start, he recalls when he, dressed as Sir Livingston, met Tricia McMillan (Zooey Deschanel), dressed as Darwin. They hit it off from the start until Trisha suggested that they take a trip to Madagascar together. When he realized that she was serious, Arthur hesitated, stating that he couldn't just up and leave his job, which left Trisha feeling deflated.
They were then interrupted by a blonde-haired man in fancy clothes who told Trisha that he was from another planet and asked if she'd like to see his spaceship. Trisha left with the man, leaving Arthur to wonder about the man's sanity and if he'd just missed a great opportunity. Ford buys a round of drinks for everyone in the pub before stating that they only have minutes before the end of the world. Remembering his home, Arthur runs out the door.
The bartender (Albie Woodington) asks Ford if the world really is going to end and if they should cover their heads. Ford responds, "If you like", though he admits that it won't help in the slightest. Arthur returns home to find that the construction crew has already destroyed his house as a looming shadow covers the area. In his sorrow, he fails to see what the construction crew is already running from; an enormous, cubed spaceship from which a harsh voice emanates over loudspeaker.
The alien introduces himself as Jeltz (Richard Griffiths) of the planning council and explains that Earth has been scheduled for demolition and that its inhabitants shouldn't be the least surprised since the plans have been on display at the local galactic planning department for 50 years. He then makes the order to commence destruction as the whole world panics and the last of the pub's patrons (including Su Elliot) places a bag over their heads.
Ford catches up to Arthur and takes a towel from what used to be his bathroom before grabbing hold of him. He explains to Arthur, now shockingly aware of the skyscraper-like ship above them, that a Vogon constructor fleet has descended on Earth to destroy it to make way for a hyperspace bypass and that he is going to hitchhike them off the planet. Ford extends his thumb from which a peculiar ring emits a yellow beam of light.
From a far away view of Earth, we see that thousands of Vogon ships have surrounded the planet in precision formation and, all at once, vaporize it in a clean, fell swoop. Our kindly narrator then returns with a proper introduction of the Hitchhiker's Guide to the Galaxy, probably the most successful, popular, and controversial book in existence. Containing countless bits of information on the universe, the book is a plethora of knowledge and assures any first-time reader with 'DONT PANIC printed in large, friendly letters on its cover'.
Ford and Arthur come to in a washroom on one of the Vogon ships. Arthur is given his towel by Ford who explains that a towel is one of the most important and useful items any hitchhiker can employ and that he must never lose it. He gives Arthur his copy of the Hitchhiker's Guide to the Galaxy of which Ford is a writer and proceeds to use his towel to break a pipe through which he attempts to signal another ship with his hitchhiking ring.
Meanwhile, Arthur educates himself on Vogons which are, as it turns out, not evil, but rather terribly structured and bureaucratic creatures. According to the Guide, "they wouldn't even lift a finger to save their own grandmothers from the Raveneous Bugblatter Beast of Traal without orders signed in triplicate, sent in, sent back, queried, lost, found, subjected to public inquiry, lost again, and finally buried in soft peat for three months and recycled as firelighters. On no account should you ever allow a Vogon to read poetry to you."
In preparation for his future intergalactic travels, Ford fits Arthur with a small, yellow, slug-like creature which he shoves through his ear and into his brain. The creature, as the Guide explains, is a Babel Fish which consumes brainwave energy and excretes conscious frequencies, allowing the host to understand any language he hears. Before Arthur and Ford can figure a way to escape, the Vogons detect their presence and bring them further into the ship for interrogation.
There, Jeltz reads to them a bit of poetry he's written, something that sends Ford into convulsions while Arthur is merely bewildered; apparently Vogon poetry is the third-worst in the galaxy. Arthur attempts to flatter Jeltz with what he thought of his poetry, but his words have no affect and Ford and Arthur are sentenced to expulsion from the ship. They are thrown into the void of space where they hover for a split second before another ship emerges and picks them up, oddly morphing from one random object to another before settling on its original form.