 After returning to Basel, Servetus published "Two Books of Dialogues on the Trinity" () which caused a sensation among Reformers and Catholics alike.John Calvin alerted the Inquisition in Spain an order was issued for his arrest.Calvin and Servetus were first brought into contact in 1546 through a common acquaintance, Jean Frellon of Lyon; they exchanged letters debating doctrine; Calvin used a pseudonym as "Charles d' Espeville" and Servetus used the moniker "Michel de Villeneuve."