During the Third Age of Elven Princes of Lower Earth, a band of noble warriors – Vidar the Elf Lord (Boyd), Penthiselea the Warrior Princess (Winkleman) and Dean the Dwarf (Eldon) – plan to save Lower Earth from the evil rule of Lord Darkness by searching for the Sword of Asnagar, "for whoso'er wields the sword shall rule all of Lower Earth." However, they first have to discover "The Chosen One" who will lead them to the Sword, whose name is "Amis". Amis is a dog belonging to Sam Porter, a misanthropic fantasy novelist in the real world.
Vidar, Penthiselea and Dean travel via a portal to take Amis, who is with Sam at a book signing in Totnes High Street, to Lower Earth. When they take Amis, Sam follows them and both Sam and Amis arrive in Lower Earth. When they arrive in Lower Earth, Amis is transformed into a human (played by Lamb), retaining many of his canine traits, such as becoming excited when there is a knock at the door, and being totally devoted to Sam. Sam believes he has been kidnapped by deranged fans until he sees the world outside the room in which he awakes. He asks to be sent back home, but is told that the portal is closed and can only be opened by the same Sword of Asnagar that Amis must seek.
Sam decides to travel with Amis, Vidar, Penthiselea and Dean to find the Sword. Meanwhile, Lord Darkness (Alistair McGowan) is planning to stop them from finding the Sword, helped by his evil but dimwitted assistant Kreech (also played by Eldon). Sam proves invaluable in using his modern instincts to trick his way past various creatures barring their way. For instance, he bluffs a three-headed troll guardian of Darkness' fortress in the same way as he would a security guard at a nightclub, distracting it long enough for Dean the dwarf to attack. He also tends to expect secret tunnels and concealed doors because that's the sort of thing he would have written into one of his plots. He is often right.
One of the writers, Gupta, said in an interview with the BBC Comedy website that ElvenQuest is not designed to be a spoof of Lord of the Rings, because this had already been done in an earlier radio sitcom, Hordes of the Things. He also said that: "we wanted to create a show which would exist in its own right. In the best sitcoms the comedy should come from the characters and their inter-relationships, which means they can't simply be two dimensional parodies."