In the Anthony Horowitz novel The Devil and his Boy, Dr Mobius is the main antagonist. He is the titular devil. He employs Tom Falconer to be the role of the boy in his play, The Devil and his boy. But unbeknown to him, Tom is the great-grandson of Queen Elizabeth I, the woman he is set to kill.

He was sent out from Spain and formed an organization named the Garden Players, which were real. Dr. Mobius was part of the Spanish Inquisition, a classic disguise because nobody expected it. He pretended to be a playwright in London hiring actors. When Tom met Shakespeare and was told nobody wanted him in the play, Tom felt disappointed, and then he met Dr. Mobius who said he'd been badly treated and he could "sense talent". Tom agreed to work with Mobius, and, as he did so, Dr. Mobius' sleeve fell down and Tom saw a brand on the man's wrist shaped as an eye with a cross. Dr. Mobius tried to hide the brand, but not before Tom had taken it to memory.

Tom was introduced to the Garden Players - Francis, Frances, Philip, Florian, Fynes, and himself. Florian was Dr. Mobius' nephew. They all lived on a derelict ship in the Thames. It was then Tom asked what happened to the boy before him and Dr. Mobius admitted the boy, Frank, had drowned. So they got on with rehearsing the new play, The Devil and his Boy, and suddenly a government agent turned up, called Sir Richard Brooke, who was a greedy, ambitious traitor. He had decided to kill the Queen along with Dr Mobius' help. Sir Richard managed to get the Players a night to perform the play, and although the play went good, the clerks were unimpressed. 

Tom found some pitchforks and remembered how Dr. Mobius had been furious with him when he dropped one. He suddenly saw they had different barrels - and saw they were rifles, and Dr. Mobius would shoot them as part of the act, but he would shoot them right at the Queen. So, Tom decided to save her. He jumped on her and Dr. Mobius shot Tom. Dr Mobius then afterwards shot a courtier. The Queen was safe, but Dr. Mobius was taken, along with Philip, Florian and Fynes, to the Tower of London. His head was later chopped off for treason. However, his nephew, Florian, was released, because when the Queen found out Tom was her grandson she saved him from his execution, and she allowed him to ask Florian to be released because there was evidence he was innocent.