The lunatic's curse

The town of Opum Oppidulum is home to the freezing Lake Beluarum and its rumored monster. On an island at the center of the lake is an asylum from which no one has ever escaped. So how will Rex, whose father, Ambrose Grammaticus, has been imprisoned there under false pretenses, prove that Ambrose is not insane? And if Rex can free his father, will his evil stepmother drive them both to madness?