Prince Septimus in the Book

     In the book, Prince Septimus is referred to more commonly as Lord Septimus. He is said to be ruthless, "the most dangerous man you will ever meet," in the words of his own brother, the eldest Lord Primus. He is often associated with blankness; his face is always blank, so as to hide the cunning therein. In the book he is described as being a poisoner; while apparently skilled in the arts of swordsmanship, he finds it inconvenient and overbearing. As far as the story goes, Septimus, along with Primus and Tertius, is summoned to the side of his dying father. There, he learns that in order to become the next Lord of Stormhold, he must retrieve his father's necklace, which is subsequently thrown from a high window.

     Having killed two of his brothers (Quintus and Sextus respectively), he is greatly feared by both Primus and Tertius, who would have made an alliance had the circumstances been different.  Septimus goes on to poison Tertius to death, causing Primus to go into hiding.  Primus however is later killed by the Witch Queen, who slits his throat. Septimus later finds his brother's corpse, and realizes that  he will now be the Lord of Stormhold, provided he avenge his brother's death.

    Septimus consequently pursues the Witch Queen, observing her carefully.  He eventually decides to kill her by means of fire.  A surprisingly skilled arsonist, her home is engulfed in flames very quickly. However, the Witch Queen calls upon the aide of one of her charms, a red cobra bracelet, that comes to life and bites Septimus in the heel. He is fatally poisoned, and dies a slow and painful death, spanning from evening to morning in length. He joins his brothers in the afterlife, and newly reconciled, they leave together in search of new beginings.

Prince Septimus in the Film

     Radically different than his book counterpart, Prince Septimus of Stormhold does not bother with concealing his cunning-he's the most dangerous, most powerful man in Faerie, and everyone knows it.  He wages war without batting an eyelash, and is the clear favorite of his father (this is even so in the book, as his father remarks that he hopes it will be Septimus who ascends the throne), who discreetly asks him to kill Secondus.  His father thrwos his amulet out the window, saying whichever son retrieves it will become the new Lord of Stormhold.

     With a party for accompaniment, Septimus sets out  South in search of the stone.  However, he later learns that he has been misled by a traitorous sootsayer, who he consequently kills.  Later on he forges a alliance with Tristran, as they both must face the Witch Queen, but for different reasons. Unlike in the book. Septimus appears interested in attaining Yvaine's heart in addition to the stone.  On the basis of this alone, it can be argued that he is more of a villain even than an anti-hero in the film.

     However,  the Witch Queen kills Septimus by drowning his voodoo entity, later using his dead body to battle Tristran, albeit unsuccessfully.  Later as the souls of his brothers ascend to the heavens, his can be seen sinking to an unknown location.