King Rat

A London man is enrolled by the King of Rats to assassinate the Pied Piper of Hamelin who dethroned him. The man is Saul, whose rat mother joined humanity, making him immune to the piper's call. In his rat persona Saul eats garbage and climbs walls. Saul is hauled out of bed by the police and charged with hurling his father from a top-floor window. While lying dazed in a cell, he is visited by a sharp-featured stranger who leads him on a gravity-defying escape. After introducing himself as Saul's uncle, King Rat, he explains Saul is half rat.