"Slayers: The Book of Spells" is a three-episode OVA series that serves as a prequel to the main "Slayers" anime, providing additional context to the adventures of Lina Inverse and her companions. The narrative is structured as a series of interconnected vignettes, each exploring a different incident from Lina's past, framed as stories recounted by Lina herself.

The first episode, "The Scary Chimera Plan," revolves around Lina and her companion Naga the Serpent encountering a mad scientist named Rezo the Red Priest. Rezo is conducting experiments to create chimeras by fusing humans and monsters. Lina and Naga infiltrate his laboratory, leading to a chaotic confrontation that highlights Lina's resourcefulness and Naga's flamboyant personality. The episode blends humor and action, showcasing the duo's dynamic as they thwart Rezo's plans.

In the second episode, "Jeffry's Knighthood!," the focus shifts to Lina's encounter with a young knight named Jeffry. Jeffry aspires to become a hero but lacks the necessary skills and confidence. Lina, initially dismissive of his naivety, becomes involved in his quest to rescue a kidnapped princess. The episode explores themes of bravery and self-discovery, with Lina inadvertently mentoring Jeffry as they face off against a band of thieves. The story balances lighthearted moments with a touch of character development for both Lina and Jeffry.

The final episode, "Mirror, Mirror," delves into a more mystical and comedic scenario. Lina and Naga stumble upon a cursed mirror that swaps their personalities. The resulting chaos forces them to navigate their altered identities while dealing with a mischievous sorcerer who seeks to exploit the mirror's power. The episode emphasizes the comedic chemistry between Lina and Naga, as their usual roles are reversed, leading to humorous misunderstandings and eventual teamwork to break the curse.

Throughout the OVA, Lina Inverse remains the central figure, with her sharp wit, formidable magical abilities, and occasional greed driving the narrative. Naga the Serpent serves as a foil, her over-the-top theatrics and rivalry with Lina adding a layer of comedic tension. The episodic structure allows for self-contained stories that expand on Lina's character and her world, offering fans a deeper look into her adventures before the events of the main series. The tone is consistent with the "Slayers" franchise, blending fantasy, comedy, and action in a way that appeals to both new viewers and long-time fans.