Like the rest of the cast, Septimus is the spitting image of his actor, Liam O'Brien, with the only discernable difference being his garb. Septimus is depicted in a smart, white button-up with a cravat, overlayed by a black-and-grey striped vest and completed by a black tailcoat. The only adoring he appears to wear is a blue and silver pin on his left breast-pocket connected to a chain that crosses over his chest and under his right collar.
Septimus Goodfellow is the alias of the Irish charlatan Archie. He found fame masquerading as an English spiritualist, but he is in fact a fraud deep in debt. He owed a large amount of money to an organization known as the Golden Dawn.
Septimus was hired by Rupert Merriweather to retrieve a casket during a Cat Show at Crystal Palace. He ventured into Crystal Palace with Alexandra O'Neil, Captain Bentley Badger, Hanako Hayashi, Dr. Mason Pocket and Ida Codswell. He placed a bet that his cat would win the Cat Show, but only did so because he had previously bribed the judges to ensure that it would win.
As the night progressed, he used his supposed spirtual powers to warn people of spirits, not to touch certain items and that the room was "turning." He, however, eventually dropped the act when actual supernatural threats began to manifest and was the first to suggest they just run.
He and Captain Badger retrieved the casket. But, Archie was so scared that he abandonned Badger and fled, taking the only lantern the pair had with him. He briefly considered charging through the glass to get outside before rejoining the group.
As the group fled through the Crystal Palace, he once again broke away from them and attempted to make it to the entrance. The rest of the group watched in horror as he vanished into the shadows and his decaptiated head rolled out.
He was later seen as one of the monsterous shadow people chasing and attacking the group. He would have been eventually been defeated and trapped in the casket by Rupert Merriweather.
Bathsheba is the cat Archie entered in the cat show. He later revealed she is not his cat, and the show was fixed for her to win.