After being transported to the Middle Ages at the end of the previous film, Ash Williams is captured by Lord Arthur’s men, who suspect him of being an agent for Duke Henry, with whom Arthur is at war. He is enslaved along with the captured Henry, his gun and chainsaw are confiscated, and he is taken to a castle. Ash is thrown in a pit where he kills a Deadite and regains his weapons from Arthur’s Wise Man. After demanding that Henry and his men be set free, as he knew it was a witch hunt, and killing a Deadite publicly, Ash is celebrated as a hero. He grows attracted to Sheila, the sister of one of Arthur’s fallen knights.
According to the Wise Man, the only way that Ash can return to his time is through the magical Necronomicon Ex-Mortis. Ash then starts his search for the Necronomicon. As he enters a haunted forest, an unseen force pursues Ash into a windmill, and he crashes into a mirror. Small reflections of Ash in the mirror shards come to life, with one becoming a life-sized clone, after which Ash kills and buries it.
When he arrives at the Necronomicon’s location, he finds three books instead of one, and has to determine which one is real. Realizing at the last moment that he has forgotten the last word of the phrase that will allow him to remove the book safely – “Klaatu barada nikto” – he tries to mumble and cough his way through the pronunciation. He grabs the book and begins rushing back. Meanwhile, unknown to Ash, his ruse has failed and the dead and his evil clone resurrect, uniting into the Army of Darkness.
Upon his return, Ash demands to be returned to his own time. However, Sheila is abducted by a Flying Deadite and later transformed into one. Ash becomes determined to lead the humans against the Army, and the people reluctantly agree. Using knowledge from textbooks in his 1973 Oldsmobile Delta 88 and enlisting the help of Duke Henry, Ash successfully leads the medieval soldiers to victory over the Deadites and Evil Ash, saves Sheila, and brings peace between Arthur and Henry. The Wise Men tells him how to return to the present by giving him a potion after reciting the phrase.
Back in the present, Ash recounts his story to a fellow employee at an S-Mart department store. As he talks to a woman who is interested in his story, a surviving Deadite, allowed to come to the present because Ash again forgot the last word, attacks the customers. Ash kills it using a Winchester rifle from the Sporting Goods department and exclaims “hail to the king, baby” before passionately kissing the woman