Each season of The Last Kingdom is based on at least two books from Bernard Cornwell's novel series, The Saxon Stories. The Last Kingdom enjoyed huge success on Netflix for five seasons before wrapping up its story with a feature film, The Last Kingdom: Seven Kings Must Die. The Last Kingdom has become one of Netflix's key franchises since it acquired the show in full from the BBC in 2018.
The Saxon Stories is an enormous series, spanning 13 novels and covering decades of medieval British history. This required The Last Kingdom to cram multiple novels into each season in order to cover the whole series. Naturally, some storylines had to be cut for The Last Kingdom, but the show does a fair job of keeping up with the novel series' most important plot points. The Last Kingdom: Seven Kings Must Die spans the final three books in the series, meaning the other 10 are covered in varying levels through the five seasons of The Last Kingdom.
The Last Kingdom Season 1
The Last Kingdom season 1 covers the first two novels in Cornwell's series, The Last Kingdom and The Pale Horseman. The story in the show is strongly similar to the story in the novels, covering the childhood of Uhtred and how he came to be raised by Danes despite being born a Saxon lord. Both the show and the books then follow Uhtred's journey to becoming a sworn-sword for King Alfred and his role in helping Alfred and the Saxons defeat the Danes and maintain control of Wessex. Both The Last Kingdom season 1 finale and The Pale Horseman end with a Saxon victory at the Battle of Ethandun.
The Last Kingdom Season 2
The Last Kingdom season 2 is based on the next two novels in Cornwell's Saxon Stories, The Lords of the North and Sword Song. The story told in The Last Kingdom season 2 begins to distance itself from the novels more than the previous season did, however, the events still line up in rough order. Both The Last Kingdom and the novels follow Alfred's attempts to set up a puppet king in Northumbria and then the defense of Mercia from the Viking brothers, Sigefrid and Erik. Both continuities end with Sigefrid's and Erik's deaths after Erik's love for Aethelflaed causes them to fall out and Uhtred saves Aethelflaed.
The Last Kingdom Season 3
The Last Kingdom season 3 is based on books 5 and 6 from The Saxon Stories, The Burning Land and Death of Kings. Both the show and the novels follow Alfred's declining health and Uhtred's struggle with Skade's curse. Alfred dies in The Last kingdom season 3 and at the end of Death of Kings, marking the beginning of Edward's reign and the loss of one The Last Kingdom's most fascinating characters. While they take slightly different paths to get there, both The Last Kingdom season 3 and Death of Kings end with the Battle of the Holme.
The Last Kingdom Season 4
The Last Kingdom season 4 follows books 7 and 8 of The Saxon Stories, The Pagan Lord and The Empty Throne. The events in The Pagan Lord are mostly crammed into the first four episodes of The Last Kingdom season 4, culminating with a Saxon victory at the Battle of Tettenhall. The next six episodes follow the conflict over the Mercian succession that occurs in The Empty Throne after King Aethelred is mortally wounded at Tettenhall. The story then shifts to Sigtryggr, though this storyline is vastly different in the show, which has Sigtryggr temporarily conquer Winchester rather than be defeated at Ceaster, as he is in the books.
The Last Kingdom Season 5
The Last Kingdom season 5 follows the 9th and 10th books of The Saxon Stories, Warriors of the Storm and The Flame Bearer. The Last Kingdom season 5 heavily alters the source material. Sigtryggr's brother, Rognvaldr, for instance, is a variation of Sigtryggr's brother from the books, Ragnall. Much of The Last Kingdom season 5 is an invention of the show because there are too many differences created by the first four seasons for the show to follow the same narrative to the letter. That said, the series did manage to adhere to the original books when it came time to wrap things up. Both book 10, The Flame Bearer, and The Last Kingdom season 5 end with Uhtred finally reclaiming his ancestral seat of Bebbanburg.