Piccadilly was a cheeky young grey mouse from the city who was born a year before Arthur and Audrey Brown on the 19th of February. His mother and father were killed by an underground train when he was very young.
He finds his way to the Skirtings, where he grows to love Audrey. His kindness is returned by nothing but cruel words, for Audrey couldn't forgive him for surviving and never attempting to save her father. He becomes friends with Oswald Chitter or 'Whitey' as he calls him, as well as Arthur and Twit.
He plays a minor role in The Crystal Prison, in which he leaves the Skirtings after Audrey inadvertently hurts his feelings.
He returns in The Final Reckoning, as the Minister of War in Holeborn, the mouse community where he lives in the city. He finds that Morgan is still alive and being referred to as 'Old Stumpy.' He has been building an army of rats from the city. Piccadilly is ready to fulfill his vow, but before he can do so, Morgan and his army take over Holeborn and kill the mice living there.
After returning to the Skirtings, Piccadilly sets off with Arthur and Thomas Triton to the Power Station to kill Jupiter. After seeing the skin of his friend Marty from Holeborn, Piccadilly challenges Morgan and they fight, but in the end, the rat commits suicide. Thomas is wounded by an ice spear and Arthur takes him back to the Skirtings, while Piccadilly goes to try to defeat Jupiter alone, but he is killed.
He returns one last time as a ghost and kisses Audrey before being led by Albert Brown to the afterlife.
(Note: Piccadilly was Audrey Scuttle's first love interest in, The Dark Portal.)