insanity

Now, you must agree that these are indubitable symptoms of insanity.”

He remained in his cell, and this visit only increased the belief in his insanity.

“Well, then,” resumed Faria with a bitter smile, “let me answer your question in full, by acknowledging that I am the poor mad prisoner of the Château d’If, for many years permitted to amuse the different visitors with what is said to be my insanity; and, in all probability, I should be promoted to the honor of making sport for the children, if such innocent beings could be found in an abode devoted like this to suffering and despair.”

"Insanity was more plausible.