The Third Key of the Architect that was wielded by Lady Wednesday (commonly known as "Drowned Wednesday"), until it was claimed by Lord Arthur. The Third Key holds control over the Border Sea. The Third Key takes the form of a trident. It is capable of changing size in relation to the emotions of the wielder (For example, anger makes it grow larger). Lady Wednesday apparently used it as a fork.
The powers of the Third Key are numerous, and as such not all of them are known. The known powers of the Third Key are;
- General Control over Fluids
- Hold backing/banishing Nothing
- Can be used to control the weight of the holder (this function was used by Lady Wednesday only)
- Lifting objects
- Can be used to walk on the surface of water
As of Lady Friday it is said that all Keys can kill anything the wielder wishes, be it Nithling, Denizen, Superior Denizen or Mortal. It is beleived that any being not of those categories, such as The Architect, The Old One and their three children (Lord Sunday , The Mariner, and The Piper) would be unphased by any such attempts. Towards the end of the series, it is thought Lord Arthur would be immune as well. It is unknown if the Trustees were immune while wielding their Keys.