Geronimo Stilton is a famous mouse who manages the newspaper "The Rodent's Echo" on Mouse Island. He enjoys writing books and spending time with his family, including his sister Tea and cousins Benjamin and Trampita. In the book "Geronimo Stilton and the Ghost of the Subway," Geronimo and his friends investigate a reported cat ghost in the subway tunnels of Ratonia but discover it is just one of Professor Voltio's experiments.