Skulduggery Pleasant's skull, also known as the Murder Skull, was a key item in the fourth book, Dark Days. Valkyrie Cain used it as the Isthmus Anchor to get Skulduggery Pleasant back from the Faceless Ones' universe.
Skulduggery had his head stolen by Goblins. Around the year 1987, Skulduggery was hired to investigate a church plagued by "angry spirits." He found out that Goblins infested the church. Skulduggery set up camp, waiting for them to arrive at the church. The first night he leapt out screaming and throwing fireballs, hoping to scare them away permanently. The second night, he crept up behind them and repeated his actions. However, on the third night, the Goblins approached Skulldugery's camp instead and stole his head while he was "meditating." Skulduggery did not realize this until the morning.
He acquired another skull by means of a poker game.
Events that Followed
Skulduggery said that the Goblins ran into a sorcerer named Larks, who took the skull from them. It was then bought by a women as a wedding gift for her husband. She then used the skull to kill her husband after figuring out he was stealing her assets. The murder was picked up by mortal police, and the skull was given the nicknamed the "Murder Skull." The skull found its way to the black market and changed hands four times. A sorcerer named Umbra, sensing the magic inside, claimed the skull. Afterward, a man called Thames Chabon acquired it.
Valkyrie, hoping to use Skulduggery's skull to save him from the Faceless Ones, managed to arrange a meeting with Thames through the vampire, Caelan. However, Chabon sells her a fake, selling the real skull for triple the price to Davina Marr.
In the Sanctuary
Davina Marr, the new Prime Detective, bought the skull to keep the portal between dimensions from reopening. Valkyrie, along with Fletcher Renn, Tanith Low, and Ghastly Bespoke, try to steal it from the Repository, but get captured in the process. Valkyrie managed to steal it with Fletcher, but leaves Tanith and Ghastly behind. She, Fletcher, and China Sorrows go to Aranmore Farm, where they are able to reopen the portal and bring Skulduggery back from the realm of the Faceless Ones.
Skulduggery now wears his original skull. He claims the one he won from the poker game is now a "spare." Twice it has been mentioned that his skull's cheekbones are higher than that of his former skull.