The blade was first discovered in Martin Chatwin's book at the Library, which described the blade as being able to slay almost anything, and that it hadn't been recovered by Martin after having been made. It is later shown that Quentin and Julia, after having travelled back in time over 70 years, have the blade commissioned by a blacksmith that a young Martin takes them to.
When Julia, Marina and Martin finally confront Reynard with the knife, they are interrupted by Penny, who runs into Julia and Martin, and teleports them to Fillory, causing the knife to fall to the floor. We then see Marina and Reynard both reach for the knife. When Julia returns to Marina's apartment, Marina is shown dead on the floor while Reynard and the blade were nowhere to be seen. It is currently unknown exactly what happened to the Leo Blade.
The blade also exists in the 23rd timeline and had been used to kill the Beast (Quentin) of that timeline.
The blade can only be touched by master magicians. Its high concentration of magical power burns anyone who is not powerful enough to wield it. It has been stated that the blade is powerful enough to kill any magical creature, even a deity.
- The creator of the Leo Blade also made the Virgo Blade.
- The blade takes approximately 70 years to make, due to the special properties of the moonstones.